Rainwater harvesting or R.O. Filters: Which is better for dry zone villagers?


By Ranjit Mulleriyawa

Drinking water obtained from open dug wells and tube wells (bore holes) in many dry zone areas contain high levels of Fluoride, Calcium and Magnesium salts. This water is believed to be a possible factor contributing to Chronic Kidney Disease of Uncertain Aetiology (CKDu). Thus, there is an urgent need to provide people living in these areas with clean drinking water to prevent further spread of this kidney disease.

Collecting rainwater running off the roofs of houses is one way of obtaining clean drinking water. Another method is to purify ground water using Reverse Osmosis Filters (R.O. Plants). Which of these is more appropriate, viable and sustainable for dry zone farming communities?


Any realistic effort to solve a problem must consider the context (setting) within which the problem exists. What then is the context of CKDu affected villagers?

* Poor people (mostly farmers), living in widely scattered rural households.

* Limited access to public services (health care, sanitation, agricultural extension etc.).

* Relatively low level of education.

* Dilapidated roads.

* Average rainfall of approximately 1000 mm per year with almost 75 % of it occurring within four months (October, November, December and January). Recent years have seen considerable variability in above distribution pattern.

* Limited ground water resources, already over exploited by haphazard construction of agro-wells for irrigation.

Household water requirements

Average household consisting of five persons is estimated to require about 20 liters of water per day (for drinking and cooking purposes).

Rainwater harvesting

Rainwater harvesting is a strategy advocated to mitigate the impact of climate change (resulting in short periods of intense rainfall followed by long drought). It is also a simple means of obtaining good quality potable water.

* Rainwater collected as runoff from the roofs of houses needs to be stored for use during the six to eight months of dry weather (February- September).

* A storage tank having a capacity of 5000 liters is adequate to tide over eight months.

* This facility (including gutters and down pipe) will cost Rs. 50,000/= per household.

* It requires no maintenance cost (except replacement of gutters once in five years or so).

* Cost of one liter of rainwater (approx. 0.25 cents) over a ten year period.

* Rainwater harvesting does NOT make any demands on groundwater aquifers.

* It is simple and easy for rural people to understand, implement and sustain.

* It does not entail dependence on external resource persons.

* Households have independent and ready access to potable water at an affordable price (0.25 cents per liter).

Reverse Osmosis Filters (R.O. Plants)

1. A single high capacity R.O. Plant can supply the daily water requirements of many households.

2. Heavily dependent on imported technology.

3. They are expensive to install and maintain requiring skilled technicians to ensure effective functioning of the filter membrane. R.O. Plants currently established cost approximately Rs. 2 million each.

4. Require electricity, water pumps, pressure pumps, expensive filter membranes and dug wells. Large R.O. plants also require buildings to house them.

5. Effluent water carrying toxic substances is allowed to go back into the environment (adding to further contamination of ground water). National Environment Act No 47 of 1980 prohibits discharge of effluents containing over 2mg/l (2 ppm) of Fluoride into surface water bodies (drainage canals etc). Feed water entering R.O. plants in CKDu endemic regions of the NCP frequently exceed 2 ppm Fluoride. Effluent water, discharged from RO plants in such areas, is, therefore, likely to contain Fluoride levels exceeding the maximum permissible limit stipulated by the Environment Act.

6. Are wasteful of water. For every liter of purified water, approximately one liter of water goes waste as effluent.

7. R. O. Plants depend on ground water (wells) as water source. Within the prevailing context of already over exploited ground water reserves, limited storage capacity of the ‘regolith aquifer of the hard rock region’ (a characteristic feature of the ‘dry zone’) , further stress on precious groundwater reserves is fraught with danger. What will be the ecological consequences of heavy groundwater extraction by a large number of high capacity R.O. plants?

8. Reverse Osmosis facilities tend to be established in centralized locations (Schools, Hospitals and Community Centers). Villagers have to collect their water requirements (almost daily) from here. This is inconvenient.

9. Organizations currently providing R. O. water levy a charge of Rs. 1.50 to 2.00 per liter of water. This is six to eight times the cost of a liter of rainwater. A family of five persons, needing 600 liters per month, will have to spend Rs. 9 00-1,200 for R.O. water. Can poor rural households afford this expenditure?

10. Are R.O. Plants sustainable within the current ecological and socio-economic context of dry zone farming communities?

11. What are the consequences for the National Economy of installing and maintaining several R.O. plants costing 8,000-10,000 U.S. $ each?

*The writer has been a farmer, researcher, and rural development activist interacting with farming communities in the dry zone for over 30 years. He holds a Masters degree in Agriculture from the University of the Philippines. He may be contacted at: rangoviya2013@gmail.com

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