discussion_rwater

Bangladesh Environment Network

In July 1999, there was a discussion in BEN regarding rainwater harvesting. The detailed discussion can be followed in the BEN discussion site, http://www.listserv.emory.edu/archives/ben.html. An imperfect summary is given below.

1. WASA is doing a pilot project on rainwater harvesting at their office in Dhaka. A report on this project is yet not available. However, WASA is currently "treating" the harvested rainwater and using it as potable water.

2. Issues: What kind of treatment is WASA providing? Is it removing pollutants picked up by the rainwater from air pollution in Dhaka? What is the cost of rainwater harvesting system? can this be duplicated by other offices.

3. Can we use rainwater harvesting in rural areas on either an individual family system or as a whole village? Individual family (or office)systems can be modeled after systems currently existing in other places like Texas, Sri Lanka and Maldives. A whole village system is also feasible.

4. Rainwater harvesting equipment and process configuration. --Individual family/office system: collection area (roof), plumbing to carry the water to a storage tank, treatment (filtration, disinfection, other treatment), distribution, maintenance. --Whole village system: collection system (pond?), pump, storage tank, treatment (filtration, disinfection), distribution, maintenance.

5. Issues: --Using chlorine for disinfection, particularly in the rural areas can be a health hazard and not practical. Can use household bleach (5% chlorine). This is safe and is being used in some areas of Mexico to disinfect domestic water. Can use ultraviolet radiation to disinfect. Should consider cost of replacing the UV light bulbs on a regular basis, and the cost of electricity. -- Space (land) is limited so can not use ponds for collection/storage. Consider using existing ponds if feasible. -- Pond liners would be expensive. Consider concrete liners -- Consider floods during construction of ponds -- Consider cost of individual systems. They may be cheaper than the pond system -- Consider air pollution, and groundwater intrusion (for unlined pond system) -- Cost of any of these systems should be evaluated based on local labor and what equipment is available locally.

Q: (Saleh Tanveer)

If we use a lined pond followed by a sand filter or a settling tank (to remove solids), subsequently process the collected water with chlorine:

(1) What are the costs involved?

(2) Is handling and storage of chlorine going to be a problem in the rural Bangladesh contexts?

(3) What size of storage tank is optimal? How many people can be served with that kind of storage capacity ?

(4) Are there some world bank or UNDP sponsored feasibility project that anybody knows about? If so, is there a website where the report summaries (if not the whole report) can be accessed?

(As is common in Bangladesh, it wouldn't be suprising if some study has been already conducted with the report gathering dust in somebody's office).

A: (Anise Ahmed)

I would think that cost would really vary with the system. However, a cost per unit gallon can perhaps be established.

1. cost of excavating a pond. I think most villages have ponds and any cost associated with excavating may have to do with dredging an existing pond to remove sediments or to excavating deeper into an exiting pond to provide additional holding capacity. This maybe done by the villagers themselves.

2. Cost of liner. Really depends upon what kind of liner you want to use, or whether you want to use a liner at all. Liner is necessary where there is a potential for contaminated groundwater to enter the pond or where it is decided to totally eliminate groundwater intrusion to keep the water "soft". If no liner is used this cost would be zero. Although there are many kinds of liners (HDPE liners, compacted clay liners, etc) and there are pros and cons associated with each one of them, I feel that what would work best in Bangladesh is concrete liners with minimum reinforcement. A 6-inch concrete liner with a 2/8 steel reinforcement square mesh at 12-inch center to center (to prevent shrinkage cracks) would be my suggestion. Cost can be established with the going rate for concrete, steel and labor in Bangladesh.

3. Cost of filter. We could use sand filter. However, there are maintenance issues, the filters have to be backwashed or changed at regular intervals of time. I would suggest using floating suction filters that float near the surface of the water in the pond. This prevents bottom debris and sediment from entering the pump and the storage tank. I will obtain cost from a vendor in USA. However, it would be good if someone can find the cost of such a filter in Bangladesh.

4. Cost of pump. Again the cost of pump should be obtained from Bangladesh. The pump should be float activated so that if the level of water in the storage tank falls to a predetermined level, the pump is activated. For complete automation I would also suggest a small pump for addition of chlorine every time the storage tank is being filled. A 1/2 horse power pump should suffice depending upon how high the storage tank is. The tank should be sufficiently elevated for gravity flow to the distribution system and the individual home outlets, if one should be present. Otherwise the villagers should just come to the storage tank and fill-up containers.

5. Cost of storage tank. Really depends upon usage. I would suggest a concrete tank or a fiberglass tank (these are now available in Bangladesh) since galvanized tanks available in Bangladesh are quite small to be used in a village. Again, some one in Bangladesh should find the local cost. Cost would of course vary with the size. In USA the average consumption is approximately 120 gallons per person per day. However, this number includes watering lawns etc. In Bangladesh I would say the water consumption should not be more than 30 to 50 gallons per day per person. So, for a 100 people village you need a 5000 gallon tank. This would be a 8x8x10 ft tank.

6. Cost of chlorine. I agree with all who noted that handling of chlorine is not practical in villages in Bangladesh. When I mentioned chlorine, I was thinking more in terms of bleach rather than pure chlorine. What is the cost of household bleach in Bangladesh? Someone in Bangladesh can answer this. Household bleach contains 5% chlorine. You want to maintain approximately 0.1 mg/L residual chlorine. It is very easy to calculate how much bleach to add for each tank volume.

7. maintenance cost. The pond should be emptied and cleaned once a year to prevent algae from growing. This can be done by the villagers themselves.

Q: (Joanna Kirkpatrick)

Can we compare the costs to government of supplying fuel, for boiling water in villages, as compared to supplying and storing chlorine? I wonder how safe it would be for chlorine to be stored in villages, given the usual settlement and climatic conditions.

A: (AA) I am sorry I was not clear in my previous e-mail. I was not thinking about using pure chlorine. I was thinking about using household bleach that has 5% chlorine. I have used this in water storage tanks in an orphanage (in Mexico, where I volunteered) where we found e.coli and it worked perfectly.

Q: (Muhit Rahman)

Could we design a container, made of local materials that limits evaporation and is small enough to be readily portable and can be considered an individual solution for much of our people?

On a per capita basis, there is about 2,000 sq. meters of surface space in Bangladesh. Assuming (an average) rainfall of 60 inches per annum (or 2 meters), and a daily "potable water" need of 1 gallon per capita and no losses due to evaporation one needs a container of approximately 0.75 sq. meters in surface area to capture sufficient precipitation to see himself/herself through the year. Although, in reality, precipitation varies greatly through Bangladesh, the math is scalable. While pollution is a big issue, it is, at least in the airborne form, primarily an urban issue. And much of Bangladesh's population (as well as land) is rural.

Q: (Saleh Tanveer) Is there some data available about the relative effects of different pollution sources in different water bodies in Bangladesh ?

A: (Anise Ahmed)

Although direct ambient monitoring of water bodies can throw light on what is "really" happening, and the ministry of environment (or some other entity) should really take upon themselves to evaluate the existing conditions of the surface waterbodies, there is plenty of scientific evidence as to what can happen if certain pollutants reach the surface waterbodies. I guess I will try to mention some scenarios in the spirit of attempting to give direction to what should be monitored.

** A major source of surface water contamination is sewage. This may be from stormwater runoff from both urban and rural areas, latrines discharging directly on the rivers, failing septic systems and groundwater contamination (which eventually reaches the surface water), and perhaps improper treatment of sewage at "wastewater treatment plants". Three major problems are associated with human sewage. 1. "biochemical oxygen demand". Human sewage contains organic matter that is degraded by bacteria in the receiving water that need oxygen for this process. Thus, there is oxygen depletion as a direct result of sewage discharge to surface waters. The oxygen depletion results in a reduction of the number of fish a water body can support. Sometimes this can even result in fish kills. The oxygen depletion also results in anaerobic conditions that result in unsightly and odorous conditions. The problem is more serious in summer when bacterial activity is high because of higher temperatures. This is also the time when rainfall is intense and more sewage enters the surface waters from storm water runoff. The problem is also acute in winter since the rivers are flowing at their lowest levels, and latrines are still adding sewage to the water; and even though the temperatures are cooler (but not freezing) bacterial activity is still present.

2. Pathogens. As we know fecal coliform bacteria is used as an indictor for pathogens. When fecal coliform bacteria are high the water body should not be used for swimming/bathing, fishing etc.; of course the water cannot be used for drinking without disinfection. In USA, surface water bodies where fecal coliforms are found at elevated levels are prohibited from any public use/access. Even shell fish (including shrimp) harvesting is prohibited. The jurisdiction for such closure lies with the Department of Health. An evaluation of the fecal coliform bacteria count in lakes, ponds and rivers would greatly help us to envision the current "pathogenic" status of our water bodies. making water pathogen free should be our goal and need.

3. Aesthetics. Who wants to swim, fish or drink water (even after disinfection)that has floating sewage in it. As mentioned earlier, oxygen depletion can cause anaerobic conditions resulting in bad odors etc.

** Pesticides. Pesticide are known to cause cancer at certain exposure dosage and time. here is a list of few pesticides: DDT (and its metabolites), Endrin, toxaphene, parathion, heptachlor, etc. It will be good to establish what pesticides were being used in Bangladesh and to find alternative "environmentally safe" pesticides that degrade readily before reaching the victim. Who or which branch of government keeps an eye on the use of pesticides in Bangladesh. Once we know what pesticides are being used we can recommend how best to manage these. One other issue is the safety of people that apply these pesticides. What is the regulatory mechanism that ensures the safety of workers that apply pesticides. In USA this is implemented by OSHA (occupational safety hazard authority).

** industrial contamination. WE are aware of the science of the effects of the various pollutants on humans and animals from industrial sources. Following is just the tip of the iceberg. 1. building and insulating materials production and handling: asbestos (causes cancer), vinylchloride (causes cancer), CFCs (causes ozone depletion) 2. Chemical and plastic production: chromium, arsenic, dimethyl phthalate, etc. All these have effects on human health or are toxic to fish. 3. Electrical industry. PCBs, chlorobenzene, vinyl chloride, etc. 4. Cosmetics, perfumes, and lotions: ammonia, chloroform, phenol, formaldehyde, xylene, methyl ethyl ketone, etc. 5. furniture making: acetone, benzene, kerosene, vinyl chloride, etc. 6. Glass manufacture: arsenic, formaldehyde, etc. 7. paint and dye shops: acetone, PCBs, nitrophenol, dioxane, etc. 8. Pharmaceuticals: arsenic, formaldehyde, mercury, bromoform, etc. 9. Photography: cyanide, formaldehyde, etc. 10. printing industry: chloroform, isophorone, etc. 11. textile industry: arsenic, benzene, formaldehyde, ammonia, etc. 12. Other industries that are present in Bangladesh are: tanneries, steel mills, jute mills, etc.

Listing all the pollutants is beyond the scope of this e-mail. However, it should be noted that all the pollutants associated with industries may not reach the surface waterbodies or ground water if they are managed properly. In USA the term used is "cradle to grave" meaning the pollutants must be managed from the time they are created in an industrial process until an environmentally safe method/place of disposal is found for them.