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Evaluating household water treatment options: health-based targets and performance specificationsProject Overview
Joe Brown (LSHTM) & Mark Sobsey (UNC)
24 October 2010, Chapel Hill
Water and Health: Where Science Meets Policy
Outline
• Technology selection and microbiological effectiveness as a piece of the puzzle
• WHO goals in creating this document– How we envision this guidance could be used
• Approach to setting performance targets– General principles– Derivation of tiered system
• Testing protocols• Context in the world of HWT• Next steps for the document
Which technology is the best?
• It’s complicated
• It depends on the context
• It depends on your point of view
• No easy answers here
HWT technology selection/choice
Implementers, NGOs• Sustained, correct
use by users• Cost • Effectiveness in
reducing microbes/chemicals
• Demonstrated health impacts
• Other factors
Users• Acceptability and
accessibility, user friendliness
• Cost • Aesthetic qualities• Delivery of clean, good
tasting water that is healthier & “better” than other sources
• Other factors
Why does effectiveness matter?
• HWT is intended specifically to reduce pathogenic microbes in water
• No feedback mechanism available to most users
• Links with public health impact, which is the point of HWT
WHO goals
• Protect users, promote public health• Provide sector guidance
– Useful international performance benchmarking• Advantages over other international protocols (but not
intended to replace or supercede others)
– Implementers, NGOs, private sector, individual users, government, etc
• Create a flexible framework that is adaptable in national verification/certification programmes
• Encourage development and use of more effective technologies
Primary audiences of document
• (i) national-level certification organizations;
• (ii), regulatory authorities;
• (iii), those involved in developing and evaluating technologies, including universities and researchers; and
• (iv), manufactures and implementers of small-scale water treatment technologies
Interpretation
• Regulatory agencies or national authorities can interpret these guidelines and apply them to specific situations of local relevance in regard to water quality and/or treatment technologies.
• The underlying principles forming the basis for this document are those set forth in the GDWQ, and may be applied where appropriate in product certification, pre-intervention performance evaluation, or technology selection
www.who.int
Guiding principles• Technologies should be as effective as possible against all
classes of microbes: bacteria, viruses, protozoa• Technologies that do not meet the WHO recommended
risk-based target from the Guidelines for Drinking-water Quality (10-6 DALYs per person per year) may still contribute to reduction in waterborne disease risk
• Technologies that do not consistently reduce all classes of microbial pathogens to a minimum extent should be recommended with caution
• Technologies that are supported by epidemiological evidence of positive health impacts should continue to be recommended for use
• Assessing microbiological effectiveness is an important part of technology selection
• Microbiological performance is not relevant if the technology is not used
Approach
• Assumptions for background water quality are used where no extensive and locally relevant data are available
• Use of quantitative microbial risk assessment (QMRA) models
• Recommended levels of performance are calculated
Background water quality data
• These guidelines use published data on reference pathogens as assumed “background” water quality data
• Reference pathogens: Campylobacter jejuni, rotavirus, Cryptosporidium
• Dose-response risk models used to then calculate how effective technologies must be to reduce disease risk
• Local data may be used but usually not practical
Reference microbe
Assumed infectious microbes per litre in untreated wastewater
Assumed wastewater content of untreated drinking-water (percent)
Assumed infectious microbes per litre in untreated drinking-water
Cryptosporidium 103 0.01% 1
Campylobacter jejuni
104 0.01% 10
Rotavirus 103 0.01% 1
Computation of log ( and %) reduction of microbes to achieve risk targets
Units Cryptosporidium Campylobacter jejuni Rotavirus
Raw water quality (CR) Organisms per litre
1 10 1
Treatment effect needed to reach tolerable risk (PT)
Percent reduction 99.998685 99.99896 99.9989
LRV required 4.88 4.98 4.96Drinking-water quality (CD) Organisms per
litre1.32 x 10-5 1.04 x 10-4 1.10 x 10-5
Consumption of unheated drinking-water (V)
Litres per person per day
1 1 1
Exposure by drinking-water (E) Organisms per day ingested
1.32 x 10-5 1.04 x 10-4 1.10 x 10-5
Dose response (r) Probability of infection per organism
0.20 0.019 0.59
Risk of infection (Pinf,d) Per day 2.67 x 10-6 1.99 x 10-6 6.53 x 10-6
Risk of infection (Pinf,y) Per year 9.74 x 10-4 7.26 x 10-4 2.38 x 10-3
Risk of diarrhoeal illness given infection (Pill|inf)
0.7 0.3 0.5
Risk of diarrhoeal illness (Pill) Per year 6.817 x 10-4 2.177 x 10-4 3.466 x 10-5
Disease burden (db) DALYs per case 1.47 x 10-3 4.60 x 10-3 1.40 x 10-2
Susceptible fraction (fs) Percentage of population
100% 100% 6%
Disease burden (DB) DALYs per year 1 x 10-6 1 x 10-6 1 x 10-6
Log10 reduction values (LRVs)
• 1 log10 = 90% reduction, 2 log10 = 99%, 3 log10 = 99.9%, 4 log10 = 99.99%, and so on
• Major outcomes from testing• Standard metric for technology performance
under challenge conditions• Calculated from log10 concentrations of microbes
observed in untreated/treated water• Provides a comparative basis for technology
selection
LRV required based on untreated water quality
0
1
2
3
4
5
6
7
8
9
0.001 0.01 0.1 1 10 100
Microbes per litre in untreated water
Log 1
0 re
duct
ion
requ
ired
to m
eet 1
0-6
DA
LYs/
cap/
year
Rotavirus
C. jejuni
C. parvum
Table 7.3, GDWQ
Rating Log10 reduction* required: bacteria
Log10 reduction* required: viruses
Log10 reduction* required: protozoa
Highly protective. Achieves WHO-recommended risk-based target of 10-6
DALYs per person/year.
≥ 4 ≥ 5 ≥ 4
Intermediately protective. Achieves intermediate risk-based target of 10-4
DALYs per person/year, representing improved water quality.
≥ 2 ≥ 3 ≥ 2
Minimally protective. Meets minimum microbiological criteria for providing improved quality drinking-water.
≥ 1 ≥ 1 ≥ 1
Typical longitudinal water quality data
0
100
200
300
400
500
600
700
800
900
1000
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103
109
115
121
127
133
139
145
151
157
163
169
175
181
187
193
199
205
211
217
223
229
235
241
247
253
259
265
271
277
283
289
295
301
307
313
319
325
331
337
343
349
355
361
Mic
robi
al c
ount
per
lite
r, as
sum
e 1
liter
per
day
Days (one year)
Risk threshold
0
100
200
300
400
500
600
700
800
900
1000
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103
109
115
121
127
133
139
145
151
157
163
169
175
181
187
193
199
205
211
217
223
229
235
241
247
253
259
265
271
277
283
289
295
301
307
313
319
325
331
337
343
349
355
361
Mic
robi
al c
ount
per
lite
r, as
sum
e 1
liter
per
day
Days (one year)
Risk threshold may be lower for some groups
0
100
200
300
400
500
600
700
800
900
1000
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103
109
115
121
127
133
139
145
151
157
163
169
175
181
187
193
199
205
211
217
223
229
235
241
247
253
259
265
271
277
283
289
295
301
307
313
319
325
331
337
343
349
355
361
Mic
robi
al c
ount
per
lite
r, as
sum
e 1
liter
per
day
Days (one year)
153 high risk days
0
100
200
300
400
500
600
700
800
900
1000
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103
109
115
121
127
133
139
145
151
157
163
169
175
181
187
193
199
205
211
217
223
229
235
241
247
253
259
265
271
277
283
289
295
301
307
313
319
325
331
337
343
349
355
361
Mic
robi
al c
ount
per
lite
r, as
sum
e 1
liter
per
day
Days (one year)
0
100
200
300
400
500
600
700
800
900
1000
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103
109
115
121
127
133
139
145
151
157
163
169
175
181
187
193
199
205
211
217
223
229
235
241
247
253
259
265
271
277
283
289
295
301
307
313
319
325
331
337
343
349
355
361
Mic
robi
al c
ount
per
lite
r, as
sum
e 1
liter
per
day
Days (one year)
90% reduction, 103 high risk days
99% reduction, 39 high risk days
0
100
200
300
400
500
600
700
800
900
1000
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103
109
115
121
127
133
139
145
151
157
163
169
175
181
187
193
199
205
211
217
223
229
235
241
247
253
259
265
271
277
283
289
295
301
307
313
319
325
331
337
343
349
355
361
Mic
robi
al c
ount
per
lite
r, as
sum
e 1
liter
per
day
Days (one year)
99.9% reduction, 4 high risk days
0
100
200
300
400
500
600
700
800
900
1000
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103
109
115
121
127
133
139
145
151
157
163
169
175
181
187
193
199
205
211
217
223
229
235
241
247
253
259
265
271
277
283
289
295
301
307
313
319
325
331
337
343
349
355
361
Mic
robi
al c
ount
per
lite
r, as
sum
e 1
liter
per
day
Days (one year)
99.99% reduction, 1 high risk day
0
100
200
300
400
500
600
700
800
900
1000
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103
109
115
121
127
133
139
145
151
157
163
169
175
181
187
193
199
205
211
217
223
229
235
241
247
253
259
265
271
277
283
289
295
301
307
313
319
325
331
337
343
349
355
361
Mic
robi
al c
ount
per
lite
r, as
sum
e 1
liter
per
day
Days (one year)
99.999% reduction, 0 high risk days
0
100
200
300
400
500
600
700
800
900
1000
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103
109
115
121
127
133
139
145
151
157
163
169
175
181
187
193
199
205
211
217
223
229
235
241
247
253
259
265
271
277
283
289
295
301
307
313
319
325
331
337
343
349
355
361
Mic
robi
al c
ount
per
lite
r, as
sum
e 1
liter
per
day
Days (one year)
Why the pursuit of greater performance then?
• Modest microbial reductions can prevent disease, sometimes dramatically– Basis for the “minimally protective” tier
• Higher risk waters and outbreak situations are the “design case” for HWT: these situations require a more effective barrier– Emergency use
• Water quality can change rapidly and new risks can arise
• The highest tier, “most protective”, meets WHO risk-based target for drinking water quality
Rating Log10 reduction* required: bacteria
Log10 reduction* required: viruses
Log10 reduction* required: protozoa
Highly protective. Achieves WHO-recommended risk-based target of 10-6
DALYs per person/year.
≥ 4 ≥ 5 ≥ 4
Intermediately protective. Achieves intermediate risk-based target of 10-4
DALYs per person/year, representing improved water quality.
≥ 2 ≥ 3 ≥ 2
Minimally protective. Meets minimum microbiological criteria for providing improved quality drinking-water.
≥ 1 ≥ 1 ≥ 1
Guiding principles for technology-specific testing protocols
• Protocols should result in data that demonstrate effectiveness of HWT technologies against bacteria, viruses, and protozoa.
• Different technologies require different approaches to demonstrating performance.
• Protocols should be rigorous but flexible. Options should exist to enable protocols to be adapted to new technologies, alternative test microbes, and different contexts, as long as scientifically credible evidence is the result.
• Laboratory testing should closely model actual field use. • Protocols should be locally developed or adapted. • Protocols should be accompanied by an appropriate
institutional framework.
Recommended protocols• Technology specific and flexible
– May be based on local capabilities and resources
• Based on actual field use conditions
• Intended to capture life cycle of longer-use technologies
• Microbes and low-cost methods are now accessible to a reasonably equipped lab anywhere in the world
• Spike in microbes to challenge waters
• Assay influent and effluent water, approximating use conditions and cycle of use for technology
• Log10 reductions are calculated:– LRV = log10(Cuntreated/Ctreated)
Suggested target/test microbes
• Target microbes (basis for QMRA)– Campylobacter jejuni
– Rotavirus
– Cryptosporidium
• Test microbes (lab surrogates)– C. jejuni, V. cholerae, E. coli others
– Rotavirus, poliovirus, bacteriophages, others
– C. parvum, E. histolytica, spore-forming bacteria (e.g., C. perfringens), inert particles
Suggested test waters• Challenge water quality
– Representative range of conditions
– Includes default values, e.g.:Test water 1(best case)
Test water 2(worst case)
Description High quality groundwater, surface water, caught
rainwater, or other water free of disinfectant residual
High quality groundwater, surface water, rainwater, or other water
free of disinfectant residual + 1% primary wastewater effluent,
sterilised or pasteurized
Turbidity < 5 NTU > 30 NTU
pH 7.0 – 9.0 6.0 – 10.0
Temperature 20oC ± 5oC 4oC ± 1oC
Can use locally relevant conditions
Protocols should be accompanied by an appropriate institutional framework• Lab and testing requirements
• Reporting and data QA/QC
• Technically competent review
• Labeling, communication of findings
• …and microbiological performance is only the beginning, one piece of the puzzle
Additional factors of potential use in setting national-level performance
guidelines• Field microbiological performance• Health impact• Evidence of correct, sustained use• Safe storage• Chemical performance• Flow rate• Taste, turbidity, aesthetic factors• Acceptability of existing evidence• Many other factors outlined in document
Labelling• WHO does not endorse or certify drinking-water treatment
technologies. Can’t use the WHO name or logo• These guidelines may provide the basis for national
certification programmes that do engage in product certification and/or labelling.
• Requirements for labelling of products may be locally developed and should be approved by regulatory agencies at the national level.
• Guiding principle: Labelling should supply enough information for consumers to make an informed choice. – Comparing options– Other reportable quantities may also be locally required, for
example: flow rate or volume per day, expiry date or duration of use if applicable or indicator of expiry, and other supporting information.
Where do HWT technologies stand now?
Disinfection/coagulationHousehold slow sand filtration
Fiber and fabric filtersDiatomaceous earth filters
Thermal treatmentUV irradiation
Solar disinfectionFree chlorine disinfection
Settling/sedimentationPorous ceramic filtration
0 1 2 3 4 5 6 7 8 9Log(10) reduction of microbes
Bacteria
Viruses
Protozoa
Sources: Souter et al. 2003, Lantagne 2001, Sobsey 2002, Hijnen et al. 2004, Timms et al., Kaiser et al. 2002, Colwell et al. 2003, Huq et al. 1996, Logsdon 1990, Schuler et al. 1988, NAP 1997, Sobsey 1989, Batchley and Peel 2001, Walker et al. 2004, Meyer and Reed 2001, Reed 1996, Wegelin et al. 1994, Mendez-Hermida et al. 2005, CDC 2001, CDC.gov 2005, Brown and Sobsey 2005, Sobsey and Brown 2006.
Next steps for this effort
• Public comment period
• Publication
