How to ensure protection from water-borne diseases in new water
We are raising money for the provision of a water system to a village in Nepal and would like advise on ensuring safety from water borne diseases,
The project involves the piping of water from an existing natural well to a tank at the top of the hill from whence it will supply the toilets and sinks of a school and the village.
We would like advise on how we can ensure the water can be made germ free or, on how the users should be trained to avoid the various chemical and biological risks which may be inherent in the supply and its storage.
We wondered if you could help us with your experience in such matters.
* Update *
I have attached:
-Drawing of the pumphouse to be built
-Drawing of the storage tank The spring used for water
-Google earth photo showing path from the pumps to the storage tank at the school.
Note that the water is obtained from a spring not a well. Villagers use this spring at the moment and tell me that water quality is good for them to drink after allowing water to settle in the carrying vessel. The plan is to store rainwater from roofs in a separate tank to supply toilets (although not in dry season).
The main issue I have is the possibility of bacterial growth in the holding tank contaminating the drinking water for the whole village and school.
Plan page 1:
Plan page 2:
Posted on behalf of George and Barbara by Pauline at REDR .
My first thoughts are as follows :
The water should be initially tested to find out what harmful levels of chemicals /other there may be. Micro-biological and chemical testing of drinking water quality should be performed to indicate whether water is safe to drink.
These can then be treated appropriately with either dosing, filtration or other treatments as required. The water tank could be a good point for any dosing, however other solutions may be more appropriate such as ground tanks.
(Commonly Chlorine with a contact time ie exposure time of the water to the chlorine, has been used to ensure germ free water delivery in UK).
Please be reminded that the water quality for sinks will be higher than toilets, if separate delivery methods can be accommodated (possibly a second untreated or less treated water tank and pipeline for the toilets in addition to a fully treated supply for the sinks etc). I appreciate the cost of this may render it inappropriate.
Ensuring the natural well is as well protected as it can be from contamination is very important, as is the training of a local well manager who maintains and ensures protection is not compromised.
Such protection methods could be concrete casing around the top section of the well, a concrete lid with a outlet pipe for the water. All outlets should be protected so nothing can crawl or be dropped in the supply. Any ground around the well or outlets should be maintained to prevent any accidental contamination at point of delivery also.
Without knowing more about the spring location and type it is difficult to describe exactly what the set up should be ie. If the pump should be sat on top of the lid for easier maintenance or whether you could incorporate a filter bed within the well.
However if you could provide us some more information and any photos or topographical details you have we would be pleased to be able to answer your specific problem as accurately as we can rather than giving you general information on the topic.
If the water source is an open well then it is likely that there will be bacteriological contamination unless it is in a very remote area. Pauline has suggested some good precautions of capping the well and building a concrete apron around it. This may not be feasible if other people are using the well for water supply, especially if they are using buckets to draw water. This would cut down on the risks of bacteriological contamination significantly but there may be sub-surface flows to the well and you need to be very careful if there are any latrines or leaking sewage pipes nearby.
Water could be tested for faecal coliform bacteria at a public health laboratory if there is one nearby or using a portable kit such as the Oxfam Del Agua kit. There is a school of thought that says there is little point in testing water if you can do little to change the situation if the water fails the test. A simple inspection of the water source can identify with some accuracy the likelihood of bacteriological contamination without the need for testing. Shallow wells are likely to be contaminated, especially without the protection described above but deeper boreholes and natural springs are likely to be better, though this comes with no guarantees.
Biological contamination in most places is a much higher risk than chemical and causes most water borne diseases; diarrhea, cholera, dysentery etc. Globally the World Health Organisation standards are considered the minimum but in many countries these are adapted into local standards. There are a lot of different parameters that can be measured and for which there are standards and for some chemicals the standard is the minimum detectable limit. In the UK the public water supply is tested against some 200 parameters whereas on every bottle of water you will find a shorter list of perhaps 12 of the key ones, sometimes compared against the WHO standard. Testing is expensive and requires a specialised laboratory though portable kits do exist for some things. Chemical contamination may come from the water itself or from pollution from mining, industry or agro-chemicals. If the area is remote and the local water authorities have not identified any chemical contamination of the water in the area then it is probably OK.
Treatment of bacteriological contamination is generally cheaper and easier than chemical contaminants. Often a 3 stage process is used in municipal treatment plants; sedimentation, filtration and disinfection though my experience with small scale treatment plants for single institutions such as schools is not good as they are often not operated correctly. If the water is relatively clear then you could just use disinfection and chlorine is the most common way of doing this and I give more details below. Other common methods of treating small quantities of water for drinking purposes include filtration through ceramic candle filters and boiling.
Chlorination is one of the most effective ways of killing pathogens and making water safe from ... (more)
My favourite feature of centralised chlorination is that you can easily, quickly & cheaply check if your water is "safe" at any point in your network. If you still have a chlorine residual at the point of use, the chance is very high that your water isn't seriously biologically contaminated.
I'd like to think that with a well at the top of a hill, if you can adequately protect the source, you may not need coagulation & filtration. Check the turbidity*, if it is consistently below 1NTU and you don't have any chemical contaminants, then you should be OK with just 20 minutes of chlorine contact time (ideally a contact tank) before use. You could be OK as high as 5NTU, I'd recommend getting a professional involved either way.
If you are supplying a reasonable size of village, I would imagine that central chlorination would be the best value solution.
Unfortunately I could only open this link: https://files.knowledgepoint.org/uploads/13974920857639755.jpg
The most simple way to avoid bacterial growth in the holding tank would be to chlorinate the water prior to the holding tank. It would also be prudent to filter the water to avoid sludge accumulation in the tank - particularly if it is a spring, which is likely to have flashy turbidity particularly with the first strong rain events of each season.
Hi George and Barbara,
Faced with this challenge I would first check the water quality for faecal contamination. If it currently has <10 faecal coliforms per 100ml then you can be confident that it will have zero after the spring has been capped, allowed to flush out (2 weeks) and is properly protected from contamination. Physico-chemical analysis is important for due diligence. Any worrying levels will have to be addressed for the sake of health of the population. Quite how you can ensure that extraction for the school does not cause difficulty in drawing water for the local population needs to be addressed - the best way wold be to have a separate tank to buffer up a minimum volume for their use. Then you face the issue of pumping the water - always costly if using internal combustion driven pumps, always the biggest source of problems and a cause of much frustration. The source looks to be quite close to the school. One way to reduce the need for pumping would be to ask each pupil to bring a bottle of water to school each day. Not ideal but done in many places around the world. If you can supply the head difference between the school and the source along with the flow rate from the source we could see if a hydram is an option. This is a simple mechanical device that pumps water for free. Your concern about bacterial growth - if this is about algae then keeping the inside of the tank dark will combat that. Regular but not frequent cleaning and shock dosing followed by flushing out will keep the tank clean. This sort of maintenance has to be well managed and supervised - if the school is taking the responsibility then there is reason to hope it will happen - otherwise water committees are another issue. If the source proves to be emitting a lot of entrained sand particles or silt then you will need a settling tank prior to pumping and may need additional filtration at the school. If this proves to be the case then I would use a slow sand filter. Both the settling tank and the slow sand filter would need maintenance. The slow sand filter would have to be sited higher than the storage tank. OK I can see it's getting messy now ...
Best to do this a stage at a time. By protecting the spring you will improve health. Get a sample checked and go from there. This will indicate the turbidity, biological and other levels of contamination that need to be dealt with. Flow and heads would be useful to know now.
Reality check (for me): looking at the satellite image, the valley in which the 'source' sits has trees further up indicating that the roots are finding water regularly. The valley is there because of erosion so the water source is probably a point where the land falls away more sharply and the water table is breaking the surface. One ... (more)
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