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Water Filter using sand,gravel and charcoal

Dear Sir/Madam,

I am the Parish Secretary of a small RC Church and your address has been forwarded to me by CAFOD. I wonder if you can help us...?

We have enjoyed the presence and company of a Kenyan Catholic Priest for the past 7 weeks, whilst our Parish Priest has taken a holiday. During this time we have talked of many things, amongst which was my interest in giving water to those in our world who have little or none. Several conversations later, and we as a parish plan to pay for the construction of a borehole and water pump in Father Alex's village. Coincidentally, CAFOD are re-introducing their water filter appeal just at this time, which put into the mind of Father, our Parish Priest, that whilst the arrangements are made for the proposed new water well some water filters may be extremely useful in Father Alex's village, but also in the surrounding villages. I have written to CAFOD asking if it would be possible to purchase some of these water filter kits to post on to Father Alex in Kenya. Unfortunately CAFOD can't supply a kit form since the filters are built using local equipment.

I wonder if you could give us any advice or help in this project? We would like to organise and set up some water filters in Father Alex's village, and possible 13 (yes 13!!) surrounding villages that form Father's parish in Kenya, in the interim before the water well is constructed and running.

May I leave these thoughts with you to consider and "mull over" and respectfully look out for a reply sometime soon?

With many thanks for your time,

Yours faithfully,

Blessings Caroline Cass

Parish Secretary/Pastoral Assistan St. Theresa's RC Church, Biggin Hill

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6 Answers

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Could you possibly clarify what it is that you are trying to filter from the water, or give us an idea of the water source so we can try to guess what you are trying to filter?

In general, if an improved water source will become available shortly then I would imagine that disinfection is the main issue and you want to distribute single-use household water disinfection systems like chlorine tablets (Aquatabs, Oasis, etc) if the water is low turbidity, or something like PUR sachets which combine coagulation with filtration for more turbid water. Education on systems like SODIS is an alternative.

I am assuming here that you mean 'treat' when you say 'filter' (an analogy would be 'fix' and 'hammer' - a hammer is one tool used to fix things, filtration is one technique used to treat water), but if you really need filtration, you may want to consider something like LifeStraws - see this discussion.

While the body of your question doesn't mention them, I have just seen sand, gravel and charcoal mentioned in the title... It is certainly possibly to construct biosand and other types of filter locally, but if an improved water source is on its way, I would suggest that the cost, complexity & risk may be prohibitive, and you may still need disinfection in any case - sand and carbon won't remove bacteria & viruses & can in some instances increase microbial contamination.

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I have seen a number of projects using home made sand and gravel filters at household level in several countries and the one common feature they have is that they have all failed. The problem being that while they are relatively easy to construct, they have a significant management requirement which is very commonly not there at household level. While at commercial scale either gravity fed sand filters (including a level of biological treatment) or pressurised sand filters are commonly used for urban water supplies, there is trained staff to manage the systems and carry out the back-washing and surface skimming as required. Also with small systems there is a danger that water will take the easiest route down the edge of the tank, avoiding the filter medium entirely. For individual hosehold use you cannot beat a simple ceramic candle filter through which water passes from one bucket to a lower bucket. These are relatively easy to maintain and effective against bacteria if handled correctly. I have seen them in use in Kenya so they are probably available to buy there. Also they start working immediately whereas a sand filter requires time for the establishment of the "schmutzdecker" - the top biologically active layer which performs part of the treatment.

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To make things work long term there needs to be a community involvement in the project from inception and continuing with the maintenance and ultimate replacement. If I have read the message correctly you are planning to install a borehole and pump but there is now the thought that filters will be useful in a much larger area as an interim measure.

In common with others I have my doubts about the effectiveness of the filters as a parachute solution where they are suddenly introduced. If there is a local organisation that has the experience of promoting and supporting their use and they think that they would be useful then I would say great go for it. However it seems to be that this is a case of a solution seeking an application rather than the other way around.

Once the borehole is there the water should not require filtration although I am not sure how this will work for outlying villages. However there are a lot of factors to plan here such as the location and whether this provides a good supply and is easy for all to access, the type of pump and how it will be maintained. These need input from the local community.

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As indicated by others, it is important to understand why you need a filter. If the source of water is a borehole, it will be important to protect the area around the top of the borehole to prevent contaminated material from the ground surface, including dirty water, from flowing down the hole and contaminating the water source. The groundwater itself, depending on the depth and rock type in which it occurs, may have concentrations of mineral material which are not healthy if consumed over the long term. Therefore, if there are no chemistry results from nearby boreholes in the same rock type, it is very important to first conduct such an analysis of water quality and then decide what kind of treatment options, if any, are most suited.

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Information on constructing Bio-Sand filters is available at along with many other web sources. While the construction details at this site are very exacting, recognize even homemade devices, as close to the design as local conditions allow, will improve surface water sources, but may not make them as safe as western world standards. Allowing people to improve their water quality themselves, even a step or two is a worthwhile improvement. Too often we think anything less than perfection isn't worth doing. The complex, too expensive, perfect solution is the enemy of a locally appropriate technology giving a step or two in the right direction. The possible "better" beats the improbable "best". But, I also agree that the solution needs to have local acceptance and not appear to be imposed upon people. Showing people how, at low cost, to improve the quality of their drinking water allows them to make the decision to adopt the technology or not. Telling them why it would help, and showing concern without mandating implementation shows them you honor their decision making and values. If they truly value it they will make a cost contribution, even if that doesn't cover full cost of the solution (hidden subsidies can work). Other commenters are correct, if the local desire to use the technology isn't internally driven, there is a high risk that the devices will not be maintained or used for long term. The real goal is to plant seeds that lead to local demand and desire for an improvement in water quality that lasts when you are gone.

Properly constructed, a borehole water source normally should not need any filtration to improve bacteriological quality.

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While I agree that the possible "better" beats the improbable "best", it is still possible to reduce water quality and increase risk with an ill-conceived or poorly executed or operated media filter.

Martin Currie _ Aqueum gravatar imageMartin Currie _ Aqueum ( 2015-10-12 15:24:14 +0000 )edit

There are a number of resources available for household-level water treatment (HWTS) solutions on CAWST's new HWTS knowledge base here: (it's still under development).

As mentioned by others above, the key is the implementation approach, not just the technology. Feel free to contact Paul Earwaker (, CAWST's technical advisor for Kenya who has a lot of experience in HH level water treatment implementation and is familiar with the Kenyan context.

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