Backwashing-Feeding Rainwater Directly Into Openwells-Terry Thomas May 2011

Backwashing - Injection of RainwaterBackwashing Injection of Rainwater into open wells

Terry Thomas2492013@gmail com2492013@gmail.com

http://in.linkedin.com/in/terrythomasindia

BackgroundBackground• The concept- Backwashing and its practice • Works undertaken and outputs• Outcomes

F t i fl i t• Factors influencing outcomes

World Bank- India Country level Development Marketplace 2004 selected PLANET Kerala to demonstrate innovative and e a a o de o s a e o a e a dcreative ideas to improve rural services delivery in water and sanitation sector.

Idea / Triggering pointIdea / Triggering point

• What if rainwater is directly fed into open wells ?• Science says -“Water column in the well is in equilibrium

within the surrounding aquifer”within the surrounding aquifer .• “If water is drawn from the well, it is replenished with flow

from the surrounding, till equilibrium is restored”. • Hence will vice versa (of above) happens if rainwater is

directly fed into the wells ? Storing rain water in the natural aquiferq

• Will “excess water flow” into the wells dilute and aid in formation of larger fresh water lens surrounding the wells.

What is Backwashing ?

Process in practice

Water storage capacity and quality is enhanced

Enriching freshEnriching fresh water zone

Is there enough rainwater for Backwashing?

For a roof area of 40 sq meters with aFor a roof area of 40 sq. meters, with a rainfall of 3000 mm, having 90% collection efficiency, provides108000 liters of water into the well.

Considering average household demand atConsidering average household demand at 350 liters per day during summer (6 months); withdrawal totals to 63000 liters of water only.

Thus more supply of rainwater exist than demand.

What happens when rainwaterWhat happens when rainwater enters into open wells directly ?

• The rise in water level causes seepage into the surrounding aquifer thus replacing the existing high dissolved solids contained waterexisting high dissolved solids contained water with soft rainwater.

• Essentially, backwashing of well is a water y gexchange process

• Continuous process enables in the formation of a larger fresh water base with right physicalof a larger fresh water base with right physical qualities.

Community Innovation

Substituting PVC rainwater collection gutters with cement mortar strip, results 75% cost reduction. This gutter which is 4 inches high and 2 inches wide costs Rs. 30 per meter length.

Community Innovation

Existing over flow pipe from the Ferro cement tanks is simply extended into open well serving y gdual purpose. Scene from Kadalundi, Calicut

OutcomesChanges in household water use profile -Comparing summer 2004 and summer 2006

80%

100%

40%

60%Before-2004After -2006

0%

20%

0%Drinking Cooking Domestic

Cleaning Bathing Washing of

Clothes

As percentage of households surveyedAs percentage of households surveyed

Before Backwashing -Range of Total Dissolved Solids

Up to 500 ppm 501-1000 ppm 1001-2000 ppm >2000 ppm

(TDS)

40% 5% 15% 40%

Average TDS reading - 2,129 ppm

After Backwashing -Range of Total Dissolved Solids Up to 500 ppm 501-1000 ppm 1001-2000 ppm >2000 ppm

85% 10% 0% 5%

Average TDS reading - 389 ppm

Financial cost Type Roof type Cost Range Type 1 Tiled house Rs 1 200-2 000Type 1 Tiled house Rs. 1,200 2,000

Type 2 Flat terraced house Rs. 400-1,500

Type 3 Slope terraced house

Rs. 1,000-2,500

Type 4 Thatched house Rs. 1,500 onwards

1US$ = Rs.45

Capital cost per household depend

• Roof type oo type• Distance between well and collection point.

“What works” and “What does t k” d “Wh t t t”not work” under “What context”

There are 5 critical factors for the success-

• Select right time for water harvest• Adequate roof area in relation to water demand• Soil type and texture in relation to aquiferSoil type and texture in relation to aquifer• Profile of the open well in relation to water table

depth • Proximity from external threats effecting• Proximity from external threats effecting

freshwater zone’s formation and sustenance

Some cautionsSome cautions

1 Backwashing is effective only for physical and1. Backwashing is effective only for physical and chemical quality improvement. Hence well water is to be boiled before consumption.

2. Roofs needs to be kept clean and made rodent proof.

3. Open well chlorination especially after the rains is recommended.

4. Discard initial 2-3 showers

5. Sand filter for filtering the incoming water is not d d i t d l th h filt irecommended, instead a cloth or a mesh filter is

needed before letting rainwater into wells.

Reference and further info:

http://www.planetkerala.org/downloads/Backwashing_English.pdf

http://www.unescap.org/pdd/prs/ProjectActivities/Ongoing/Water/Kerala/Kerala.aspp p g p p j g g p

http://www.hindu.com/2005/08/15/stories/2005081504610300.htm

Terry Thomas

2492013@gmail.com