Aquatest: An Affordable Water Test

7/29/2019 Aquatest: An Affordable Water Test

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Aquatest: An Affordable Water Test

by

Robert Bain (G)

Fourth-year undergraduate project

in Group D, 2007/2008

I hereby declare that, except where specifically indicated, the work submitted herein is

my own original work

Signed .. Date:


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Aquatest: An Affordable Water Test | Technical Abstract i

Technical Abstract

Aquatest: An Affordable Water Test

Motivation and purpose

The project was motivated by the scale and severity of problems with water supplies in

developing countries. Every year 1.8 million deaths (of these 90% are children under five)

are attributable to poor water supplies, sanitation and hygiene (WHO, 2004). Despite

considerable effort by the international community to tackle this problem, success has been

limited; a different approach is clearly needed. Community-driven development is easier to

sustain, but the technology to facilitate the shift of power has not been developed. The

monitoring of water quality is a case in point; laboratories are centralised and portable

testing kits based on Membrane Filtration are too expensive (around 1000) for most

communities to afford. The purpose of this project is two-fold:

(i) To examine water supply, sanitation and hygiene in rural areas of developingcountries and determine whether bacteriological water testing is appropriate for

this context. And if there is a need;

(ii) To develop an affordable and easy to use bacteriological water testing device thatenables widespread water quality monitoring in rural areas.

Is water testing appropriate?

An initial literature review reinforced the need for water testing:

Surveillance and verification of drinking water quality in small community water supplies is

recognised as an essential activity; however it remains potentially complex and expensiveInternational network on small community water supply management

Alice Springs, Australia July 2005

However, further exploration cast doubts on the appropriateness of water testing. A

combination of case studies, interviews and a thorough literature review were used to

establish the need for water testing, assess its limitations and gain a better understanding ofthe context.


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Aquatest: An Affordable Water Test | Technical Abstract iii

Table of ContentsTechnical Abstract ................................................................................................................. i

List of Figures ................................................................................................................. iiv

List of Tables .................................................................................................................. iiv

List of Boxes ..................................................................................................................... v

Acronyms ......................................................................................................................... v

1 Introduction ...................................................................................................................... 1

2 Summary of the Project .................................................................................................... 3

3 Methodology ..................................................................................................................... 6

4 Part I: Exploratory Research ........................................................................................... 10

4.1 Case Studies ............................................................................................................. 10

4.2 Significance of Water Quality .................................................................................. 104.3 Alternative Measures ............................................................................................... 14

4.4 Can Testing Lead to Action? ..................................................................................... 16

4.5 Evaluation of Current Water Testing Practices ........................................................ 17

4.6 Conclusions .............................................................................................................. 22

5 Part II: Constructive Research ......................................................................................... 24

5.1 Determining Requirements ..................................................................................... 24

5.2 Critical Evaluation of the Aquatest Prototype ......................................................... 27

5.3 Experimental methods ............................................................................................. 28

5.4 Concepts and Their Evaluation ................................................................................ 39

6 Final Conclusions ............................................................................................................. 41

6.1 Findings .................................................................................................................... 41

6.2 Recommendations and Further Work ..................................................................... 42

6.3 Critical Evaluation of the Project ............................................................................. 42

7 Appendix ......................................................................................................................... 43


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Aquatest: An Affordable Water Test | Technical Abstract iv

List of Figures

Figure 1: Areas of Risk for Travellers Diarrhoea ................................................................. 1

Figure 2: Rotavirus distribution ........................................................................................... 1

Figure 3: Methodology Flow Diagram ................................................................................. 7

Figure 4: Faecal-Oral transmission paths ........................................................................... 11Figure 5: Categories of monitoring and interventions ...................................................... 14

Figure 6: Hydrogen Sulphide test ...................................................................................... 19

Figure 7: IDEXX Quantitray 2000 ....................................................................................... 20

Figure 8: Schematic of the relationship between indicator groups .................................. 21

Figure 9: Requirements Capture ........................................................................................ 24

Figure 10: Functional Diagram ........................................................................................... 24

Figure 11: Functional analysis of incubation ..................................................................... 25

Figure 12: Incubation temperature and time to get a result with the H2S test ................ 25

Figure 13: Model of Aquatest first device prototype ........................................................ 27

Figure 14: Likelihood plots for a single dilution with fifty wells. ....................................... 31Figure 15: Discrimination between threshold values using Monte Carlo ......................... 33

Figure 16: Heating and heat storage options that were considered ................................. 35

Figure 17: Incubation using body heat .............................................................................. 35

Figure 18: Bessel Function ................................................................................................. 38

Figure 19: Experiments to determine critical radius ......................................................... 38

Figure 20: Equivalence between empty submerged tube and suspended filled tube ...... 38

Figure 21: Final concept waterjet demonstration model .................................................. 40

Figure 22: Final design concept CAD drawing ................................................................... 40

Figure 23: Pipettes or sterile syringe ................................................................................. 40

Figure 24: Graph of Coefficient of Variation ...................................................................... 45Figure 25: Plots demonstrating the Most Probable Range ............................................... 46

Figure 26: Random number allocation .............................................................................. 46

List of TablesTable 1: Comparison of deductive and inductive research ................................................. 6

Table 2: Criteria for water testing to be considered appropriate ....................................... 9

Table 3: Summary of Case Studies ..................................................................................... 10

Table 4: Description of water testing methods ................................................................. 17

Table 5: Evaluation of testing kits against criteria ............................................................. 20

Table 6: Problem Definition ............................................................................................... 24Table 7: Requirements Specification ................................................................................. 26

Table 8: Advantages of MPNS over MF ............................................................................. 27

Table 9: Statistics Nomenclature ....................................................................................... 29

Table 10: Statistical assumptions ....................................................................................... 29

Table 11: Discrimination between example threshold values for a 50ml sample ............ 33

Table 12: Morphological Chart .......................................................................................... 39

Table 13: Case Study Findings ............................................................................................ 44

Table 14: Measures of Uncertainty ................................................................................... 45


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Aquatest: An Affordable Water Test | Technical Abstract v

List of Boxes

Box 1: The Aquatest Initiative

Box 2: Occupancy Theory

Acronyms

HIV/AIDS Human Immunodeficiency Virus/ Acquired Immune Deficiency Syndrome

IWA International Water Association

JMP Joint Monitoring Program

MIT Massachusetts Institute of Technology

MPN Most Probable Number

MPN Most Probable Number

MPNMD MPN-Multiple Dilution

MPNS MPN-Sample Subdivision

MTF Multiple Tube FermentationUNICEF United Nations Children's Fund

WHO World Health Organisation


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Aquatest: An Affordable Water Test | 1 Introduction 1

1 Introduction

1.1 Motivation

The motivation for the project is the scale and severity of disease related to problems of

poor water quality in developing countries. According to estimates 1.1 billion people in

developing countries do not have access to an improved supply of water; of these 84%

live in rural areas (JMP, 2006). Faecally contaminated water is one of the main transmission

routes of infectious diseases and poses a major threat to human health. Every year 1.8

million people are killed by diarrhoeal disease resulting from a lack of clean water,

inadequate sanitation and poor hygiene. Ninety percent of these are children under the age

of five (WHO, 2004).

These figures are likely to underestimate the true extent of the problem as a significant

proportion of the disease goes unrecorded (IWA, 2003); they also overlook the morbidity

caused by diarrhoeal disease which is aggravated by restricted access to healthcare,

malnutrition and the prevalence of HIV/AIDS. Diarrhoeal disease primarily affects those with

undeveloped or weakened immune systems: children, the elderly and HIV/AIDS suffers (and

travellers). Water-borne diseases are often perceived as an entirely developing country

problem (fig. 1). They are also affected by climate and are particularly prevalent in tropical

countries; the warmer, wetter and more humid climates tending to exacerbate problems

with water quality and sanitation (fig. 2).

Figure 1: Areas of Risk for Travellers Diarrhoea(Centre for Disease Control and Prevention, 2008)

Figure 2: Rotavirus distribution of cases. Each point represents500 out of a total of 800,000 yearly deaths (Glass, 1997)


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Aquatest: An Affordable Water Test | 1 Introduction 2

1.2 Approach

A new approach to monitoring is needed

Despite considerable effort and investment over the years, the international agenda to

improve water and sanitation has not seen the success expected. Furthermore, it seems

unlikely that the Millennium Development Goal for water (#7 Target 10: halving the

number of people without sustainable access to safe drinking water) will be met in many

countries the number of people without access in Sub-Saharan Africa is in fact increasing

(JMP, 2006).

As noted by the World Health Organisation the top down approach has limitations:

While global estimates of coverage will remain important, local capacity to generate and

use information will be a vital part of the monitoring effort (WHO, 2008)

The most sustainable approach would be to reduce the dependence of the poor on external

support through community-based or driven development. In many cases the infrastructure

and technology to facilitate this shift of power has not been made available; one area which

is particularly lacking is the monitoring of water supplies. This project assesses one way of

monitoring water quality: bacteriological water testing referred to as water testing below.

Water testing

Bacteriological water contamination comes from many sources much of which has little

sanitary significance. The purpose of water testing is to detect recent faecal contamination

(Hutton, 1983) and identify water that is unfit for drinking.

It is not practical to routinely test for all pathogenic micro-organisms that might be in

drinking water; instead tests should detect bacteria that are indicative of faecal pollution.

Faecal-oral disease transmission is responsible for the spread of water-borne disease and

therefore the presence of these indicator micro-organisms is thought to give a good

assessment of the health risk posed by drinking water. If indicator bacteria are not present

then the water is deemed safe to drink. The three indicators that are often used are

coliforms and more specifically thermotolerant coliforms or Escherichia coli (known as

E.coli). Bacterial densities are usually given as a number per 100ml the volume of waterusually tested.


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Aquatest: An Affordable Water Test | 2 Summary of the Project 3

1.4 Project Objectives

(i) To examine water supply, sanitation and hygiene in rural areas of developingcountries and determine whether water testing is appropriate in this context. And if

there is a need;

(ii) To develop a low-cost and easy to use bacteriological water testing device thatenables widespread water quality monitoring in rural areas of developing countries.

2 Summary of the Project

Familiarity with a low-cost water test developed at Massachusetts Institute of Technology

(MIT) led the author to the initial conclusion that an appropriate water test could be

produced for a fraction of the current price. Experience using this kit at a school in

Tocantins, Central Brazil reinforced the perceived need for monitoring water quality. The

boarding school (Fundao Bradesco Canuan) wanted to continue testing water as an

educational exercise in nearby communities, but was unable to because the test relies on

several consumables that are expensive and not available in rural areas (Section 6.3).

A brief literature review at the start of the project supported the need for low-cost water

testing (see quote above), however as the project progressed the benefits of water testing

were increasingly called into question. The initial proposal for the project was to further

develop the work carried out on the MIT water testing kit and to make it suitable for

community use. It quickly became clear that whilst this would result in a relatively low-cost

kit (at around 1/10 of the cost of commercially available testing kits such as DelAgua) it

would remain out of the reach of people earning less than $2 a day. A previous 4th

year

project (Gordon, 2006) had followed this path, achieving only incremental improvements to

the low-cost kit.

Surveillance and verification of drinking water quality in small community watersupplies is recognised as an essential activity; however it remains potentially complex

and expensiveInternational network on small community water supply management

Alice Springs, Australia July 2005


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Aquatest: An Affordable Water Test | 2 Summary of the Project 4

Part I: Is water testing appropriate for rural water supplies?

In light of the limitations of such a project, contact was made with organisations for which

an appropriate test could be developed or where the issues of water quality could be

researched. The first of these was the Karen Hilltribes Trust, a charity which builds gravity-

fed water supplies in Northern Thailand. The charity was contacted with the intention of

designing a low-cost water test that was appropriate for the Karen (one of the ethnic hill

tribes). Telephone conversations and interviews with the head of the charity led to several

interesting findings and the overall conclusion was that water testing was not appropriate

for the Karen. There were very good reasons for this including:

Mountain springs have little to no contamination and with adequate treatment(Biosand filtration) the water was known to be clean.

Volunteers had attempted to conduct water testing for the charity, but it had beenplagued by procedural difficulties and inconclusive results.

Attempts to get in contact with organisations in Northern Mozambique where water quality

problems are particularly acute (and because the author speaks Portuguese) were also

unsuccessful. It became clear that research would have to be conducted in the UK and

would have to rely primarily on secondary sources.

It was decided to build on these unexpected findings, explore case studies from secondary

sources and to conduct a thorough literature review in order to establish when water

testing is appropriate. The initial research questions were:

1 Where does water testing fit into strategies for the (improvement of) provision of cleandrinking water?

2 Is testing appropriate? If so when, and what can it achieve?3 What are the most important factors to measure? What are the best ways to do these?The case study research highlighted further concerns (technical and socio-political) and even

called into question the basic assumptions on which water testing is based ( Section 4.2.1).

Interviews and secondary sources supported these findings. Whilst water testing is seen as

inappropriate in several circumstances, it has been found that there is still a pressing need

for a low-cost device (Section 4.6.2).


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Aquatest: An Affordable Water Test | 5

Part II: Aquatest

In January 2008 contact was established with the Head of the Aquatest Initiative, Dr.

Stephen Gundry (Box 1). Working for Aquatest marked a significant change in the direction

of the project and greatly increased both its scope and potential. Large-scale manufacture

together with the development of a new field testing kit opened up the possibility of

producing a device at a cost that will be affordable to those in need. The research areas

agreed with Dr. Gundry were:

- Determining requirements for the device- Evaluating methods for incubating the device- Developing design concepts

With the results of the research outlined in Part I and criticisms of water testing in mind,

work began on these tasks (Section 5). And in addition, a statistical model was developed to

ascertain the number of wells and volumes needed to discriminate between a given set of

risk levels (Section 5.3.1).

Box 1: The Aquatest Initiative

Aquatest is a collaborative effort to design and disseminate a low-cost water testing kit for

developing countries. It is led by the University of Bristol and collaborators include WHO, UC

Berkeley and the University of Cape Town and Indian Participants.

With support from the Gates Foundation ($13.1 Million), they aim to develop a small single-

use device for an ambitious cost of $0.10. The test is to be used by water professionals and

communities themselves. It is hoped that within 10 years, low-cost water testing devices

will be widely used in 80% of developing countries (Aquatest website).

The first prototypes will be field tested in India and South Africa in 2009. Distribution and

Licensing of the technology will be led by PATH, an organisation that has experience with the

disposable syringe.


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Aquatest: An Affordable Water Test | 3 Methodology 6

3 Methodology

most people become experienced with one type of study and then stick to it, safely and

unadventurously(Hakim, 1992)

This project combines both deductive and inductive research: the former primarily in the

first half, the latter predominantly in the second. The two approaches are compared in

Table 1. The main weakness of the deductive approach, in which engineers are traditionally

trained, is that it eliminates the possibility of unanticipated findings (Eishenhardt, 1989).

Table 1: Comparison of deductive and inductive research

Deductive Inductive

Starts from General Theory

Form specific hypotheses

Numerical or statistical

Starts from Observations

Identify Patterns

Textual

Narrow

Testing and confirmation

Open-ended

Explanation of reasons

Familiarity with the MIT water testing kit meant that approaching the problem with a new

perspective was of utmost importance. Inductive approaches helped to avoid coming up

with theories at the outset. In working for the Aquatest Initiative it is particularly important

to avoid advocacy; only through questioning the benefits of water testing could substantive

research be produced (Hakim, 1992). The methodology used is shown schematically in

figure 3 on the next page.


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Figure 3: Methodology Flow Diagram


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3.1 Part I: Exploratory Research

Research was conducted predominantly through the use of inductive approaches: case

studies, interviews and a thorough literature review.

Case studies were central to the first stages of the project. Theory-building case study

research is appropriate in the early stages of research on a topic or toprovide freshness in

perspective to an already researched topic (Eishenhardt, 1989). It can be seen that both of

these applied to this research project: a fresh perspective on water testing was needed and

little research had been done to establish whether tests are appropriate for use in rural

areas of developing countries. Analysis was carried out in two parts: (i) individual case-

analysis and (ii) searching for cross-case patterns. Case studies guided the literature reviewand highlighted many issues with water testing.

Interviews were informal. They ranged from telephone interviews with the head of the

Karen Hilltribes Trust (KHT) to discussions with experienced Water and Sanitation and Public

Health engineers. Several meetings were arranged with the Head of the Aquatest initiative.

TheLiterature Reviewhad several purposes: (i) to gain an understanding of the wider issues

surrounding water quality in developing countries, (ii) to validate the case-study research

findings and (iii) to pursue lines of enquiry. An appreciation of the wider context of water

testing was seen as vital to ensure that the monitoring process is adequate, appropriate and

most of all informative.

3.2 Part II: Constructive Research

The constructive research was heavily influenced by two sources:

Good Design Practice for Medical Devices and Equipment(Shefelbine, 2002) The Inclusive Design Toolkit(Clarkson, 2007).

Conventional engineering design process focuses on conceptual design: where the most

important decisions are made (Cross, 1994). The central preoccupation is seen to be not

missing good ideas. In contrast, the primary focus of the process followed in this study was

to establish the real need and ensure that the design solves a genuine problem.


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3.3 Criteria for Success: Defining Appropriate

It is interesting to note that whilst the Aquatest device will support grassroots development

it goes against much of current development thinking. It will be mass manufactured and the

technology is not easily understood by the user (they are not able to take control of the

technology). The central notion of intermediate technology (from which the term

appropriate technology was popularised) is that it addresses the need for labour intensive

rather than capital intensive work; hence lending itself to small-scale, decentralised

workplaces (Schumacher, 1973). The definition of appropriate has changed in the light of

some very successful projects that have used modern mass-manufactured goods: examples

include mobile telephones in Bangladesh and LEDs for rural lighting.

In this report, appropriate simply means that it is suited to the specific needs of the users

and the demands of the context (in this case rural areas of developing countries). The

following criteria (Table 2) were developed during the project and have been used to

determine whether water testing is appropriate in this context.

Table 2: Criteria for water testing to be considered appropriate

1. Relevant Meaningful and sensitive to the users education, aptitude andorganising skill. Relevant to their

2. Significant Of sanitary significance established link to health outcomes3. Worthwhile it must be possible to use information from the test and this

information should not be readily obtained from another source;

4. Affordable It must be low-cost to run and have a small upfront cost5. Independent It should not be reliant on external support, or materials that are not

available locally.

6. EnvironmentallySustainable

It must not generate excessive waste at the point of use.

7. Scalable It must be scalable to facilitate widespread monitoring of drinkingwater


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Aquatest: An Affordable Water Test | 4 Part I: Exploratory Research 10

4 Part I: Exploratory Research

Is Water Testing Appropriate for Rural Water Supplies?

4.1 Case StudiesTable 3: Summary of Case Studies

Organisation Project Location Abbreviation

Karen Hilltribes Trust Gravity-fed water supply Northwestern Thailand CS1

Escola Bradesco

Solar water disinfection and

water testing using the low-cost

MIT testing kit

Central Brazil CS2

Student ProjectProposed water quality

assessmentTolla Islands, Indonesia

CS3

Vigyam AshramWater testing using the multiple

tube fermentation method.Pabal, India

CS4

Table 3 summarises the case studies used at the beginning of the project. The first two are

the authors own observations and experience and have been described briefly in the

summary. The last two were gathered from secondary sources and personal

communication. Conclusions from the case study research are given in theAppendix 7.2.

4.2 Significance of Water Quality

The extent of diseases related to water, sanitation and hygiene was described in the

introduction. A question that needs to be asked is: how much of the disease is attributable

to water quality? This has major implications for how diarrhoeal disease is tackled globally,

but at the community level and for this project it needs to be asked in order to justify water

quality testing which is inherently linked to interventions improving water quality.

4.2.1 The Importance of Water-borne Disease

The faecal-oral transmission route (fig. 4) is complex and there are many ways for

pathogens to be passed from one person to the next. An important question for anyone

trying to reduce diarrhoeal disease through environmental interventions is: which are the

dominant transmission paths?


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Figure 4: Faecal-Oral transmission paths (Prss, 2002)

Before examining the evidence, faecal-oral diseases need to be classified as water-borne or

water-washed(Feachem, 1978):

Water-borne diseases are those that are transmitted when contaminated water is drunk.

They can be prevented by improving water quality.Water-washeddiseases are caused by water scarcity; an inadequate supply of water inhibits

personal hygiene: washing hands and food. Water-washed diseases can be prevented by

increasing quantity of water without improving the quality.

If all of the diarrhoeal disease was transmitted via the water-washed route, as was

suggested by Prof. Cairncross in an interview, water quality interventions (and water

testing) would not be worthwhile. A causative link between water quality interventions and

diarrhoeal disease needs to be established in order to justify water testing. For this we turn

to Epidemiology, the study of the factors affecting health in a population.


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Review of the epidemiological evidence for water quality

Whilst there are many studies of water quality interventions, most have methodological

flaws and decisions cannot be based upon them. For example in the most recent meta-

analysis Clasen et al. (2007) rejected 947 out of a total of 979 studies reviewed. Thesemethodological problems have been well documented (Blum D, 1983).

Until recently, there was consensus that water quality and access were both important

means of reducing diarrhoeal disease; access was seen as more important than

bacteriological quality (Jensen, 2004). Interest in Household Water Treatment and Storage

(HWTS) has led to several new studies showing strong support for water quality

interventions in the household. In their review Fewtrell et al. (2005) found that water

quality interventions at the household gave a mean reduction of 39% in morbidity, whilst

those at the source only achieved 11%. Furthermore Clasen et al. (2007) found that water

quality interventions need not be combined with hygiene and sanitation to be effective.

Despite these encouraging findings, Prof. Cairncross is convinced that the water-washed

route is dominant water scarcity, not quality is responsible for the transmission of

diarrhoea. Of the four blinded studies reviewed in the paper he co-authored with Clasen

(2007) none showed reductions in diarrhoeal disease. Intervention studies which are not

blinded are liable to bias both because the researchers hope to show their treatment is

effective and because communities are likely to understate their disease because they are

grateful.

There are two main camps:

1. Those that advocate water quality interventions in the household;2. Those that advocate greater access to water;

In conclusion, the epidemiological evidence for water quality interventions is easily

challenged; there is no consensus as to the relative importance of these transmission

routes. The relative predominance is likely to be dependent on many factors, e.g. in drier

areas scarcity is likely to be dominant; in wetter and more populous areas waterborne

disease may be significant.


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4.2.2 Safe Water

There are two common principles in definitions of safe water: (i) that the water is drinkable

and (ii) that it poses little risk to health. A further principle needs to be added for a safe

water supply: access to adequate quantities. As was seen in the previous section, there is

considerable debate on the relative importance of quality and quantity.

The guideline value for bacteriological quality of drinking water is 0 Coliforms (or E.coli) per

100ml (WHO, 2006). While only a guideline value, governments often set this as a standard

to be met by all supplies despite not being affordable. This target is not achievable in most

rural areas of developing countries and does not encourage the incremental improvements

in quality and access that are needed to reduce diarrhoeal disease.

Exposure-response

Given the lack of consensus surrounding transmission paths, it is no surprise that there is

little data on exposure-response curves. Drinking water quality testing in the west has been

focused on ensuring the efficacy of treatment processes rather than measuring a health risk

thus not demanding research on the quantitative relationship between indicator density

and health outcomes. The lack of evidence is apparent when compared to the vast literature

on the health risks associated with bathing waters. It also explains the WHOs unwillingness

to suggest suitable targets for rural areas of developing countries despite much criticism.

In conclusion, there is a real need for more research before quantitative testing is

meaningful for people drinking water from sources which are not disinfected. This is also

needed for appropriate water quality standards to be set to readdress the bias towards

water quality interventions described in the next section.


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4.3 Alternative Measures

Figure 5: Categories of monitoring and interventions

4.3.1 Monitoring

Health Outcomes are the most desirable indicators because they are directly what we aim

to improve through interventions. Monitoring of the source and intervening processes is

indirect and therefore only useful if causal links between the measure taken and the desired

outcomes can be established. The main problem with measures by outcome is that they do

not usually identify actions that the community can take or locate sources of pollution.

Cholera epidemics, when all water is suspect and should be boiled are an obvious exception.

As was found in section 4.2 even with a rigorous epidemiological study, it can be hard to

isolate the impacts.

If it was always possible to know by examining the source whether water is clean, then

water testing would not be worthwhile. Unfortunately, in many cases you cannot tell

whether water from a particular source is safe to drink, let alone whether it is clean at the

point-of-use. This being said, there is much to be gained from perceptions of the quality of


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water sources, the type of source and treatment administered and the state of the water

supply. It is not surprising that the open wells tested in Brazil (CS2) were heavily

contaminated whereas the mountain springs in Northern Thailand (CS1) were clean.

Sanitary surveys are a formalized means of assessing the environmental risks they usually

constitute a series of questions with yes or no answers. A score, the number of yes

answers gives an indication of the risk. Like perceptions of quality, the current forms do not

necessarily correlate well with the actual contamination of the source. Region specific

surveys can be developed once the importance of different risk factors is understood.

Sanitary surveys are very important but require experience (Hofkes, 1983) and the user

must be literate.

One of the main advantages of a low-cost water test is that it can be used with little or no

training and could therefore be scaled up rapidly. The main weakness of water testing is

that it does not indicate possible sources of contamination or measures to improve water

supplies. Combining water testing and sanitary surveys would overcome these difficulties,

but it is not clear how this can be done without depending on expertise.

4.3.2 Interventions

Figure 5 shows that there are many interventions which can reduce the likelihood or

severity of diarrhoeal disease. Preventative measures are more ethically acceptable than

relying on treatment, especially when access to healthcare is limited (stores of Oral

Rehydration Sachets are only currently reaching 38% of 0-5 year olds in the developing

world (UNICEF, 2008)). Behavioural change in particular is often the most cost-effective way

of reducing risk, but requires trained staff and is dependent on external support.

It was generally accepted that too much emphasis has been put on water supplies

(Thompson, 2001). Feachem (1978) suggests that donors and governments both have

vested interests in water supply interventions and that there has been a degree of wishful

thinking about the benefits. With the recent findings, HWTS are becoming increasingly

popular and considerable efforts are being made in their development and dissemination.

Their development has been spurred on by very positive results in recent intervention

studies and the finding that water from improved sources is readily contaminated before


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use. There are many HWTS, these include: chlorination, solar water disinfection and ceramic

filters.

Water testing can play a role in increasing awareness of disease transmission, hygiene and

encouraging greater care for personal environment. This was its purpose in Brazil (CS2).

However, it is primarily linked to interventions to improve water quality in particular

HWTS.

4.4 Can Testing Lead to Action?

Whether water tests will lead to action to improve water quality depends on many factors.

The technology to treat water is available and in many cases affordable: it is a matter of

priorities, preferences and whether the test can be understood.

Priorities: Many people may not perceive diarrhoea as being more than an inconvenience

unless it is severe and life-threatening (Howard, 2002).Water quality is often a high priority

for women, especially mothers, but it is a much lower priority for men. Immunity means

that it is easy for adults to perceive the risk of drinking water as low. If water quality is a low

priority, it is very unlikely that a water test will be bought no matter how low-cost it is.

Interpretation:As was found in several of the case studies, many people do not share the

scientific concept of disease. Waterborne diseases are particularly prone to supernatural

beliefs. Unlike natural causes, you can drink bad water for a while before getting ill. There

is also the difficulty of blaming water when there are so many other transmission routes. If

the technology is not easily understood by the user, there is a high risk of misinterpretation.

These will need to be addressed by field testing and through careful design.

Preferences: Chlorination is heralded as a simple solution, however many people do not like

the change in taste. As noted by Zoeteman (1980) the physical characteristics of water are

often the most important for the user. More contaminated sources are drunk because of a

better taste or because they are more convenient.


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4.5 Evaluation of Current Water Testing Practices

4.5.1 Methods

The traditional method for determining faecal-contamination is multiple tube fermentation.It will be referred to as most probable number by dilution (MPND) to distinguish it from the

method used in the Aquatest Device which is MPN by subdivision (MPNS). MPND is a

laboratory based method requiring substantial quantities of reagent, glassware, distilled

water, an autoclave and large incubator (Tab. 4). Laboratory testing is particularly

problematic for remote areas of developing countries - transportation is unreliable and time

consuming making it difficult to analyse samples within the recommended 6hrs (WHO,

2006). It is also much more expensive, requires high calibre staff and the distance (physically

and organizationally) between central laboratories and rural villages means that it takes a

long time before remedial action can take place (Hutton, 1983).

The development of the Membrane Filtration (MF) and more recently chromagenic reagents

have made field testing kits feasible. The incubation requirement is greatly reduced; for MF

a single Petri dish needs incubation whereas many test tubes need incubation in the case of

MPND. MF is used by almost all commercial field testing kits, with the exception ofPresence/absence (P/A) tests which are a simplified form of MPND compromising a single

undiluted tube.

Table 4: Description of water testing methods

Membrane

Filtration

(MF)

Water is passed through a membrane (typically 45m pores) leaving the bacteria

on the filter. The filter paper is placed in a Petri dish and broth that selects bacteria

of sanitary significance is added. The Petri dish is then incubated (24hrs) to allow

these bacteria to form visible colonies. These colonies are then counted to find thenumber of indicator bacteria (Colony forming units- CFUs) that were present in the

water sample. If there are many CFUs it may become difficult to count; water that

is expected to be highly contaminated can be diluted prior to filtration in order to

lower the number of CFUs to within the counting range (around 100 CFU).

Most

Probable

Number by

Dilution

Measured volumes of the sample water are diluted and pipetted into a series of

sterile tubes containing broth. The dilution series is tailored to the expected

concentration of bacteria in the sample. Test tubes are incubated for (24-48hrs

depending on the broth used) after which the bacterial density can be inferred


24/56


(MPND) from the tubes which show growth. The most likely number of organisms is called

the most probable number and Standard Tables are available for most dilution

series.

Presence/

Absence (P/A)

Presence Absence is effectively MPND reduced to a single undiluted tube. The

presence absence test does not provide a quantitative determination.

Most

Probable

Number by

Subdivision

(MPNS)

This is similar to the MPND method, but avoids dilution. Instead the sample is

mixed with the reagent and then split into small wells. The bacterial density of the

sample is inferred from the number of wells showing positive growth. Standard

tables are not always available because the configurations differ from MT-MPN.

4.5.2 Equipment

There is a wide variety of water testing kits on the market; however most are intended for

users in developed countries. Examples of commercially available field testing equipment

specifically designed for use in developing countries include the DelAgua water testing kit,

H2S test and in development the MIT water testing kit. IDEXX Quantitray is also described

as this was the inspiration behind the Aquatest approach.

DelAgua (MF)

Developed at the University of Surrey in collaboration with Oxfam, DelAgua is probably the

best known portable water testing kit. The kit was designed primarily for international aid

workers and in particular humanitarian emergencies and reflects their needs. In addition to

measuring bacteriological contamination, the testing kit can measure a variety of chemical

properties of the water including residual Chlorine. The kit costs a total of 1327 (Institute,

2008) and approximately 0.30 per test. Even with significant subsidies it can rarely be

afforded by local NGOs, let alone communities or households. The kit is cumbersome

(weighing 10kg) and, requires training (3 days), several, often imported, consumables

(methanol, filters, pads and reagents) and an electronic incubator - all barriers to its

widespread use. The DelAgua kit is only suitable for users conducting regular testing.


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Hydrogen Sulphide Test (P/A)

At a cost of around Rs. 10 (about 12p) (IWP, 2007) this test is

the most affordable water test available. It was designed not to

require incubation and has many advantages over the MF basedtesting kits. The major limitation with the H2S method is that it

only indicates whether bacteria are present or not it does not

give a quantitative estimate. This is useful for ensuring that

chlorinated supplies are working effectively because you would

expect no indicator bacteria to be present. However, most rural

water supplies are not disinfected and have some level of faecal contamination: P/A tests

condemn too many supplies (IWA, 2003). Another problem with the H2S test is that it

detects Hydrogen Sulphide producing spores, some of which do not indicate faecal

pollution. For this reason it is not recommended by WHO (2002) a more recent study

indicates that H2S only correlates with E.coli for concentrations of over 1000/100ml (Gupta,

2007).

MIT Low-cost water testing kit (MF)

The MIT low-cost water testing kit is based on MF. The filtration device is compromised of a

baby bottle and syringe. Sterilisation is avoided by using disposable sterile inserts. The need

for reliable electric supply for incubation is circumvented by a phase change incubator: a

primary alcohol is used as a heat store and releases heat at a constant temperature as it

solidifies. Experience in Brazil suggests that the sterile inserts and reagents are not readily

available. Furthermore, the reagent used in Brazil (Millipore mColiblue24) is expensive and

requires refrigeration clearly an alternative is needed if the testing kit is to be independentof electricity.

Figure 6: H2S test

(courtesy of Susan Murcott)


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IDEXX Quantitray (MPNS)

A serial dilution is equivalent to splitting a sample of water

into small wells of varying sizes. This is the basis of the

Quantitray procedure (named MPNS in this report). This is arelatively new development in water testing practices and is

more accurate and easier to use than MF. However,

Quantitray is by no means appropriate for rural areas. It

needs an electronic incubator and heat sealer.

4.5.3 Evaluation of the Testing Kits

Table 5: Evaluation of testing kits against criteria

Criteria DelAgua MIT H2S MPNS

1 Relevant no training no training yes Yes

2

Significant yes yes

not

recommended by

WHO

if E.coli or

thermotolerant

3Worthwhile yes yes

condemns too

many supplies

if counts are

within the range.

4

Affordable no no yes

can be

manufactured at

low-cost5 Independent no no yes Yes

6 Environmentally

sustainableyes

uses many

consumables

if reused or

recycled

if reused or

recycled

7 Scalable no no Yes Yes

The review of current testing equipment suggests that it will be possible to use the principle

behind Quantitray (MPNS) to develop a water test at price close to that of the H 2S test and

is able to discriminate between contaminated sources.

Figure 7: IDEXX Quantitray 2000

(www.idexx.com)


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4.5.4 Choice of Indicator Bacteria and Reagents

Water contains many bacteria, most of which are harmless. The ability to isolate particular

groups of bacteria that are indicative of a health risk is of particular importance to the

development of a water test that meets the needs of the user. In the west, it is acceptable

to use the Coliform (Total Coliforms) group because testing is used to measure the efficacy

of treatment not to gauge health risk.

An important distinction has to be made between an indicator and an index. This has

implications for the amount of information that can be derived from microbiological water

tests.Indicators are bacteria whose presence indicates faecal contamination. An index is an

indicator whose concentration is directly related to

the health risk(Gleeson, 1997).

While many alternatives have been suggested,

Escherichia coli (E.coli) is recognised as the best

indicator of faecal contamination (WHO, 2006). It

is by far the most common bacteria in the human

gut (up to 109

per gram of faeces(Gleeson, 1997))

and is found in warm-blooded animal faeces. Figure 8: Schematic of the relationship betweenindicator groups


28/56


4.6 Conclusions

4.6.1 Discussion of the Limitations of Water Testing

It is much harder to justify quantitative water testing than was expected at the start of theproject. The main criticism of water testing is the limited evidence supporting the link

between indicator densities and health risk. To justify quantitative assessments of water

quality, the link needs to be firmly established.

Information from the water test may be used in hygiene education, but its primary use is to

ensure the bacteriological safety of water in the household. It is therefore strongly linked to

HWST and avoiding source-to-point of use contamination. Care must be taken not to further

the water quality agenda over the other preventative measures that need support: access,

hygiene education and sanitation.

Whether water testing will be a priority for individuals and communities and the value they

will put on testing is dependent on many factors these will have to be determined by field

studies. Experience in Brazil (CS2) suggests that there will be resistance where the test is not

readily understood by the community or if the scientific concept of disease is not shared.

There is a high risk of misinterpretation if the user is expected to understand the result, but

not the means by which it is found.

4.6.2 Establishing a Need for Water Testing

There is no way for households and communities in rural areas of developing countries to be

sure that the water they drink is safe. Whilst there is much to be gained from indigenous

knowledge, perceptions of quality can be misleading; they could be exposing themselves to

an unnecessary risk of illness. Water testing is attractive as one way of addressing the

question: Is this water safe to drink?

Combined with sanitary surveys, water testing would provide an effective means of

monitoring rural water supplies where contamination is expected. This would allow users to

both detect faecal contamination and identify its source. It would enable communities and

individuals to take control over their own water supply; not to rely solely on foreign aid or


29/56


the stretched government agencies which have clearly failed, in many cases, to provide

water that is suitable for consumption.

Several bacteriological water tests are commercially available, but none is suitable for

community level testing. Current tests are both too complex and expensive or they

condemn too many supplies to be of use in this context. Indeed, little has changed since

Mara (1973) noted that:

In the majority of existing water supplies in developing countries (particularly in rural areas)

facilities for the bacteriological examination of the finished water are absent.

There is a real need for widespread monitoring of water supplies in rural areas. Watertesting could offer a means in which to do this in an affordable way and with less demand

for training than other monitoring methods. There is a clear need for people who are

looking after children, the elderly or immune-compromised to assess water quality. Those

most at risk need to be able to identify ways to lower their exposure to the faecal pollution.

In the opinion of the author, this need justifies the work in the second half of the project:

working with Aquatest to develop a low cost water testing kit.


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Aquatest: An Affordable Water Test | 5 Part II: Constructive Research 24

5 Part II: Constructive Research

Development of an affordable water test

5.1 Determining RequirementsFollowing Shefelbine (2002) there are four processes that need to be carried out before the

requirements specification can be completed (fig. 9).In the second half of this report, the

focus of the design is on what is seen as the primary user: mothers. Uses by professionals

and the trade-offs for greater coverage are also discussed.

Table 6: Problem Definition

Figure 9: Requirements Capture (Shefelbine, 2002)

Figure 10: Functional Diagram

WHO? Individuals and water professionals

(Village user, Local water engineer,

community leaders and health workers,

household).

WHAT? Water quality test that is low cost,

portable, reliable

WHY? To test bacteriological quality of water

WHERE? Rural areas of developing countries: at

the source, in the home or in a clinic

WHEN? When water quality unknown and for

regular monitoring of supplies


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5.1.1 An example of functional analysis: Incubation

Figure 11: Functional analysis of incubation

The Aquatest initiative is in the process of developing a reagent for E. coli which gives a

visual signal without the need for UV light. Since the reagent has not been developed yet

the influence of temperature on incubation time is not known. Growth models were

reviewed, but it became clear that there were too many variables. An alternative approach

is simply to use known results from the H2S test (fig. 12) as a basis for setting the

requirements. As many of the H2S bacteria are E.coli, this is seen as a good approximation.

Figure 12: Incubation temperature and time to get a result with the H2S test (J. Pillai, 1997)

Requirement: Temperature shall not drop below 22C nor rise above 44C during the 36

hours of incubation. The temperature should be close to 37C.

0

20

40

60

80

100

120

14 22 28 37 44

Time(hours)

Temperature (C)


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5.1.2 Requirements Specification

The full requirements specification is listed in Table 7. It is important to note that whenever

possible, the requirements have been relaxed so that the device is not needlessly

constrained.

Table 7: Requirements Specification

able to sample from all water supplies (accessible - at point of collection) D

able to test intrinsic water quality W

Representative encourages representative sampling W

Aseptic sample is collected without being contaminated by the user D

does not require more than one day of training. D

no training required W

Maintenance does not require maintenance by user W

Ready Signal User given signal when when the test result is ready D

InterpretableUser able to tell whether the water is suitable for drinking by (i) a normal healthy adult (ii)

children under 5, the elderly and immune-compromised/HIV.D

maintains a temperature of between 22 and 44C for a duration of at least 36 hours D

incubation close to the optimal growth temperature 37 W

users warned if the incubation has failed D

Precision able to discriminate between thresholds (to be set based on epidemiological data) D

Reliability gives the correct threshold 95% of the time when used correctly D

Sensitivity sensitive to 10/100ml D

sensitive to 5/100ml W

Significant test for E.coli. Shall test for E.coli or Thermotolerant Coliforms (WHO) D

Comparable help to prioritise the contamination problem W

Waterproof not leak contents or be affected by dampness or humidity. D

able to get the device to the regions where it will be used in a cost effective manner D

small enough to fit in a pocket W

no special storage requirements D

shelflife of at least three months; if sold in boxes (3 + 2n months). W

Independentnot reliant on sterilisation, electricity, distilled water or any other resource that is not

availableD

able to be dropped 2m onto rock without breaking D

difficult for someone to open up unintentionally or intentionally by a child W

resistant to shocks and vibrations during transport D

reusable W

not generate excessive waste D

Portable easily carried to and from the source (upto 1km by foot). D

Adaptable can be used in fixed laboratory incubators W

less than $0.30 at full scale manufacture D

$0.10 delivered to the customer, the Aquatest target price. W

costing


33/56

Aquatest: An A

5.2 Critical Evaluation

It's a small, single-use devi

electricity or skilled techni

target manuf

Figure 13: Mod

1. The design is complicreaction (red) surrou

efficient way of incub

2. It is not certain wheth3. The choice of MPNS

change needed to ma

the most important o

Table 8: Advantages of MPNS ove

Lower Skill

It is easy to cont

laboratory worke

individual practice

1983). This is som

Robens Institute

Affordability MPSS is more affo

ReliabilityThe assay is more

growth of injured

Range

It is possible to t

supplies this m

dilution.

fordable Water Test | 5 Part II: Constructive

of the Aquatest Prototype

e for testing water quality. It can be used in

ians. It is being designed for use in developi

ctured cost of 10 US cents.(Aquatest Web

l of Aquatest first device prototype (Davis & Gundry, 200

ated and it is unlikely to meet the cost tar

ded by an insulating layer (yellow in fig. 1

ting the sample.

er this configuration is adequate.

is appropriate to the requirements and r

ke water testing affordable. It has many ad

which are:

r MF

minate the samples when using MF and it requir

should receive a weeks training and have an o

before he undertakes membrane filter analyses (M

ewhat of an exaggeration, but MF is not easy to u

ffer a 3 day training courses for their DelAgua kit.

dable than MF

reliable because suspended growth inherently allow

acteria (Fujioka, 1997).

ailor the device to the concentrations that are ex

ans it can detect higher concentrations than MF (

Research 27

the field, without

g countries at a

ite)

7)

et. An exothermic

) is clearly not an

presents the step

vantages over MF,

s training a skilled

pportunity for further

junkin 1976, in Hutton

se: by comparison the

s the resuscitation and

pected in rural water

ax 200CFUs) without


34/56


5.3 Experimental methods

5.3.1 Statistics for the Device

Progress was hindered without results from the Aquatest Initiative describing theconfiguration of wells that were needed in the device. In order to develop the concepts and

preliminary designs an appreciation of the how the design would affect the operational

characteristics of the test was required.

Two first observations can be drawn about MPNS:

1. More information can be gained about the concentration for a given volume if thenumber of wells is increased.

2. If there is at least one bacterium in the sample the device will show growth in atleast one of the wells. The sensitivity of the test is therefore related to the total

volume of water in the sample.

5.3.1.1 Relevance of the Statistics and Ease of Interpretation

The test must be easily interpreted and the result relevant to the user. An MPN table: a

chart which tabulates the most probable number (an estimate of the bacterial density) for

each configuration of positive wells is clearly not appropriate.The user is not interested in a

count rate, but rather an indication of the level of risk from which a decision will need to be

made. Often, this will be a drink/dont drink decision.

Both Quantitray 2000 and the Aquatest prototype have used wells of different sizes. This

may be confusing as it is not intuitive that the largest wells are the least important. It is

suggested that the wells ought to be the same size this will make interpretation easier and

increase the information gained by the test.

5.3.1.2 Literature Review

There is an extensive literature surrounding the most probable number. At first efforts were

focused on determining the most probable or most likely number, but have since turned to

the more difficult matter of defining a measure of the uncertainty of bacterial counts using

the method. It is a Standard Method and has been used widely in microbiology and

medicine since 191 (McBride, 2005). However, approximate MPN calculations, rounding


35/56


conventions and different methods of calculating the confidence limits lead to considerable

variability in the Standard Tables (McBride G. , 2003). The literature describes serial

dilutions as used in MPNMD; this is equivalent to the method used in this project as long as

the organisms are assumed to be randomly distributed.

It is helpful to introduce some notation and review the assumptions on which the calculation

of the MPN is based before describing the methods used:

Table 9: Statistics Nomenclature

R Number of wells

r Number of positive wells

s Number of sterile wells

n Number of E. coli in sample

V Total volume of sample

v Volume of a single alquilot

L (D|H) Likelihood of the data given the hypothesis

Table 10: Statistical assumptions

Assumption Description Comments

Detects one

or more

organisms.

If there is at least one organism

there is an obvious change which

can be clearly and consistently

identified.

There are many ways in which a test may fail

to detect a viable organism. If the medium is poor

it can require several bacteria and therefore

underestimate contamination.

Randomly

distributed

Bacteria are separate, not

clustered and they do not repel

each other

Supposed to thoroughly mix the sample. It is

possible to take a sub-sample that contains no

bacteria, especially if concentrations are low.

Poisson theory

or

Binomially

distributed

The volume examined is a

relatively small portion of a large

sample which had been

thoroughly mixed such that the

volume of each alquilot is small

compared to the sample volume

(v/V


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5.3.1.3 Methods

Calculating the MPN Using Occupancy TheoryEstimates for the Most Probable Number (Thomas 1942, Cochran 1950) are not suitable for

large R or multiple dilutions (McBride, 2005). While Standard Tables, simple estimates and

even an MPN Calculator (Blogett, 2003) are available the exact MPN had to be calculated.

Only with the likelihood function could measures of uncertainty be determined.

The likelihood functions were evaluated directly from Occupancy Theory (box 2) using

Matlab. It is relatively computationally intensive and the code had to be sped up in order to

calculate the likelihood functions within a reasonable time. This was achieved by creating

lookup tables thus reducing the number of times slow functions (e.g. binomial[], ln[]) were

called. Most Probable Number lookup tables were created to in order to evaluate the

operational characteristics described in section 5.3.1.6. The lookup tables were compared to

Standard tables to verify the technique.

| , = 1

Box 2: Occupancy Theory(David, 1962)

If n bacteria are randomly distributed among R test tubes of equal volume, the likelihoodthat (R-r) tubes will not receive any of these bacteria and therefore remain sterile is:

The Most Probable Number is the value of n that maximizes this likelihood.


37/56


Figure 14:Likelihood plots for a single dilution with fifty wells (top graph has seven positive wells, lower graph showing

forty). The MPN is found by selecting the largest conditional likelihood. The plots demonstrate that the test is better at

discriminating between small numbers of organisms - when many wells show growth the curve is broader.

5.3.1.4 Measures of Uncertainty

As demonstrated infig. 14, it is difficult to discriminate between MPNs when the majority of

the wells show growth. An appreciation of the uncertainty introduced by the MPN

technique is needed to design the test. This is much harder than determining the MPN and

there is no exact way to calculate the uncertainty in the MPN result. In fact the confidence

or credible intervals are subjective (McBride, 2003). One must make prior assumptions

about the likelihood of contamination in order to determine a measure of uncertainty.


38/56


Typically a diffuse prior (uniform distribution of mean bacterial densities) is used. Counter to

experience and intuition, this assumption implies that high concentrations are more likely to

be found than low concentrations.

McBride (2003) suggests that water testing lends itself to the Bayesian statistics. He

assumes the experimentalist is concerned with the probability of a particular result being

within a range. While this may be the case for scientific studies, when tests are to be

compared with risk assessments they are firmly in the classical statistical philosophy. The

device is looking for performance in the long run rather than being specific about the

current result.

5.3.1.6 Calculating Uncertainty

The most traditional means of expressing uncertainty, the confidence interval, is not strictly

appropriate for likelihoods and three alternatives were evaluated (Appendix 7.3). The

Monte Carlo Method was suggested by Prof. Spiegelhalter as a means to determine the

uncertainty of the measurement.

Operational Characteristics: Monte Carlo

From a risk profile, threshold values that the test should be able to discriminate between

can be chosen. The values chosen are (based on examples in 2 nd edition WHO Guidelines

Vol.3 (1993) pg. 78) are arbitrary: low risk (50/100ml) and high

risk (>100/100ml).

A Monte Carlo method was developed to examine the operational characteristics of

different device designs. It is described in the Appendix. This also facilitated the examination

of thresholds in line with the chosen risk levels: to establish how many wells are needed to

distinguish between chosen E.coli concentrations.


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Figure 15: Discrimination between threshold values using Monte Carlo a comparison of 25 and 50 wells with fixed total

sample volume of 50ml

Table 11: Discrimination between example threshold values for a 50ml sample

Number

of Wells

Discrimination between 10

and 100/100ml10 and 50/100ml 50 and 100/100ml

5 Good Poor None

10 Good Adequate Poor

20 Good Good Poor

25 Good Good Adequate

50 Good Good Good


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Findings and implications for the design

1. The device is looking for assured quality in a large number of different water suppliesand thus requires a frequentist approach. We are not interested in the scientific

measurement of the exact value of the MPN. The user is only interested in the

extent of contamination of the water and the resultant health risk of drinking it.

2. The MPN method is not a precise technique. When many wells show growth, there ispoor discrimination.

3. There is a trade-off between complexity of test (both design and interpretation) andprecision. It is easier to interpret the device if all of the wells are the same size.

4. The first prototype does not appear to be adequate for the purposes required.5. The high bacterial concentrations expected in source selection (often >1000/100ml)

are a challenge for a device using MPN: the well sizes would have to be very small. It

may be necessary to design two devices: one for assessing drinking water and

treated supplies and the second for more contaminated supplies such as surface

waters.

5.3.2 Energy Strategy

Purpose: to ensure bacterial growth and reliable results within a reasonable time.

In Section 5.1.1 it was found that the temperature must remain within the range 23 to 44C.

Growth is less sensitive than the precision of electronic incubators first led the author to

believe. To maintain temperatures close to the optimal and within this range, several

approaches were considered. These can broadly be termed low-tech and high-tech. The

options for storing and accepting heat that were considered in this project are described

below (fig. 16). Temperatures were recorded using an Omega 4-channel Datalogger in an

environment fluctuating between 16 and 20C. Whilst these do not reflect tropical

temperatures or diurnal variations, the results give a good indication of the approaches that

are likely to be successful.


41/56


Figure 16: Heating and heat storage options that were considered

5.3.2.2 Low-tech: Body Heat

Body surface temperature is typically between 32 and 35C, higher on some areas of the

body such as the armpits. It was soon realized that placing the device on the body gave

sufficient temperature regulation, a finding validated by experiments (fig.16). Body heat has

been shown to be a very effective solution.

Figure 17: Incubation using body heat (50ml sample)

Whilst acceptability can only be established through field trials, reports from South Africa

suggest that individuals and households will be happy to carry the device with them for the

duration of incubation (Gundry, 2008). For these users, where there is a choice between

speed of the assay and cost, the design should invariably aim for the lowest cost.

Store Energy

Chemical EnergyExothermic

Reaction

Inorganic

PCMSalt Hydrates

Sensible HeatInsulated water

bath

Latent Heat

Liquid-Gas

Vapourisation

Solid-Liquid

Melting

Organic PhaseChange Materials

Lauric Acid

T=42-44

1-Tetradecanol

T=38Solid-Gas

Sublimation

Solid-Solid

Accept energy

Solar

Biomass

Body Heat

0

5

10

15

20

25

30

35

0 0.5 1 1.5 2 2.5 3

T

emperature(C)

Time (hours)

Water Temperature

Environment Temperature


42/56


The use of body heat however is unlikely to be accepted by water professionals. They will

not want to have several water samples attached to their bodies all day and night. It is

suggested that high-tech solutions may have a role for incubating several samples at a time

or during transport to a location where laboratory incubation is available.

5.3.2.3 A Reusable Incubator?

A simple solution which could also solve the temperature requirement for professional

users is to heat water to just above the optimal temperature and warm the devices in this

water. The correct temperature could be attained by using a thermometer, or mixing three

parts boiling water and one part source water. The samples could then be stored in an

insulated container (e.g. vacuum flask) with a fraction of the warm water. This approach was

evaluated using a 0.5l thermos flask. After 33 hours the temperature had dropped from

42C to 24C, within the required limits. The main problem with this approach is the need to

boil and transport more water.

The viability of Phase Change Material (PCM) to incubate several water samples (taken as

0.5l of water roughly ten) at a time was assessed through a combination of experiments and

(lumped mass) heat transfer modelling. This began with a test of Portatherm - the incubator

used in the MIT kit. It was unable to maintain a steady temperature despite containing only

500ml of water and over 2kg of PCM: either the insulation or the mass of PCM would need

to be increased. Improving insulation is expected to be more cost effective and would result

in a lighter incubator. 1-Tetradecanol, the PCM used in Portatherm, should not be ingested

and its use is not recommended for safety reasons (note: a leading cause of poisoning in

some developing countries is ingestion of kerosene). An alternative, Lauric Acid (Tm=42C),

was found by searching through two reviews of PCMs (Farid (2003), Zalba (2002)) and the

CRC handbook.


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Findings and Implications for the Design

(i) Body heat is by far the most appropriate solution. The device ought to bedesigned so that it can be kept near the body comfortably for over 36 hours.

(ii)

Phase change materials are not a viable option for a single sample and even lessfor a single-use device.

(iii) Placing the device against the skin may not protect it from extremely hightemperatures. In this case the device could be submersed in more water from

the source and left in the shade.

(iv) A reusable incubator would be desirable for professional users who need toundertake frequent monitoring. This incubator could use phase change in an

insulated box Lauric Acid is recommended for this purpose.

5.3.3 Bubbles and Stability

Purpose: response to problem during prototyping of narrow tubes 3mm I/D. Narrow blocked

tubes would not fill when submerged in source water.

When a narrow tube blocked at one end is submerged, air cannot escape and a bubble

chamber forms. Surface tension forces dominate and water is stable above air. As the radius

is increased the gravitational forces become more important and at a certain value, the

bubble is no longer stable and the tube fills with water. This radius, , had to bedetermined because it would impact the form of potential designs, if not the minimum

volume of water that could be separated. A stability analysis can be used to describe this

phenomenon, the result of which gave an upper bound on the critical radius as just less than

5mm. Mestrel (2008) gives a derivation of the critical radius, leading to Equ. 2:

> Equ. 2

Where is the smallest value given by the Bessel function which satisfies the rigidwall boundary condition Jm(kr) = 0. Figure 17 demonstrates that this is on the (blue) J1

(curve); it has a value of 18.41. This predicts an antisymmetric perturbation as is to be

expected: air must go up one way as the water goes down the other.


44/56


The numerical result in these lecture

notes (r = 2cm) was in fact correct. The

answer above was confirmed by a second

source (Joseph, 1970) and experimentswere conducted to verify this model.

Kitchen experiments

This was a very simple experiment: holes of different diameters were drilled into an acrylic

block. The block was then carefully submerged in dyed water. Holes larger than the critical

radius filled with the dyed water: the critical radius was between the smallest tube that

filled and the largest tube that remained empty (fig 19).

Spurious initial results could be accounted for by residual soap in the water (as confirmed by

later experiments). It is useful to note that impurities (e.g. turbidity) will always weaken the

surface tension, which supports the use of the surface tension of pure water in determining

the upper bound.

Eq. 1 predicts that the stability depends only on density and surface tension. Results

supported this theory for deep wells (40 mm), but nearly all of the 10-15mm deep wells

filled. This suggests that the stability also depends on the depth of the well. The theory was

Figure 18: Bessel Function

Figure 20: Experiments to determine critical

radius

Figure 19: Equivalence between empty submerged tube and

suspended filled tube


45/56


also verified by an equivalence it implies (fig.20) between this problem and the emptying of

narrow tubes filled with water (then blocked at one end).

Findings and Implications for the Design

The trapping of air in thin wells is a limit on the smallest volume of water that can bedivided by pouring water into or submerging the device. This is therefore a limit on

the range of the MPNS method. One way around this is to pipette the water into the

device.

The diameter should be at least 10mm to ensure that the wells can be filled bysubmersion in water so that bubbles will not be stable.

By inspection, the smallest wells in the first Aquatest prototype will suffer from thisproblem.

5.4 Concepts and Their Evaluation

Table 12: Morphological Chart

Sample Reagent Incubate Make safe Dispose

Directly into

device e.g. BailerPill packet Body Heat

Solar water

disinfectionSterilise in lab

Samplecup/whirlbag

Powered Organic PCM +insulate

Chlorinedisinfection

Sterilise in field

Transfer using

disposable pipetteSaturated

paper

Body heat +

insulateBoil Generate waste

HydratedExothermic

reactionRecycle

Mixing boiling

waterBiodegradable

A morphological chart (Tab. 12) was used to explore different combinations of functions.

Having established that body heat would adequately incubate the water sample, the critical

function was taking the sample. With indicator bacteria present in the environment, it

would need to be very simple in order to make sure it is carried out aseptically. The most

promising concept is described on the next page; other ideas are given in the Appendix 7.4.


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Aquatest: An A

Final Concept: pipette transf

The Aquatest prototype wou

gloves and the device would

when opening the bag would

pipette to transfer water fro

the water, hands can be kep

stability limit described in sec

A screw-on lid with neoprene

The neoprene could be white

(shown in green) would need

due to solar disinfection, but

overheating. The screw-on li

that it is not easy to contami

and would preferably be tran

The choice of materials will b

and if so where the re-sterili

not to be encouraged both

this would impose the weste

may be difficult to impleme

further dependence on centr

Figure 23: Pipettes or stsyringe

fordable Water Test | 5 Part II: Constructive

r into the device

ld be complicated to use and relatively wa

be packaged in a sterile bag. The risk of c

be high. A much simpler solution is to use

the source to the device. As pipettes are o

clear from the device. Using a pipette also

tion 5.3.3.

under it is suggested to stop cross-contami

as shown in the figure to facilitate reading

to be opaque to prevent unintentional den

it is suggested that the colour is not dark

d should be deep, entirely encasing the si

ate the interior. The base (shown in grey)

sparent.

e determined on whether the device is exp

sation will take place. Generating waste at

ecause the collecting systems are not ava

n disposable culture. However, the autho

nt a collection scheme and furthermore t

lised laboratories.

Figure 22: Final ConceptWaterjet demonstration model Figure 22: FinaldrFigure 21: Final concept waterjetdemonstration modelrile

Research 40

teful. It would use

ntaminating these

sterile disposable

perated away from

avoids the bubble

ation of the wells.

the results. The lid

turisation of E.coli

s this may lead to

es of the base, so

ust be translucent

cted to be reused,

the point of use is

ilable and because

r recognises that it

is may result in a

design concept CADawing


47/56

Aquatest: An Affordable Water Test | 6 Final Conclusions 41

If the device is to be reused, the lid could be made from polypropylene and the base from

polystyrene, both of which are resistant to UV and can be autoclaved. A disposable device

would need to have a seal to show that the device has not been used.

6 Final Conclusions

6.1 Findings

Water testing

1. Without stronger epidemiological evidence quantitative water quality testing is onlya measure of the extent of faecal contamination: it does not measure health risk.

2. An affordable water test can be produced using the MPNS method. This will be muchmore suited to the needs of the rural poor than current equipment.

3. The significance of water quality and in particular the health benefits of improvingthe quality of water supplies have often been overstated. In spite of water quality

being important it is also essential to have an integrated approach to solving health

problems.

Design of the Aquatest device

1. Field testing kits were designed to strict specifications many of these are notjustified in this context and add unnecessary expense. Minimum requirements for

the device have been proposed.

2. Aquatest ought to pursue low-tech incubation methods: the use of body heat isdeemed appropriate.

3. Statistical models suggest that ten wells may not provide enough information todistinguish between sources. A statistical model has been developed which will

enable the configuration to be dete

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Aquatest: An Affordable Water Test