Seal of Approval

Water Filters

Water filters reduce carbon emissions by providing clean drinking water without the needing to boil it. If we know the amount of fuel a household was using to boil water before they received a filter, we can compare it to the amount used after receiving the filter, and work out how many carbon emissions the filter saves. Filters can save a family time and money on collecting or buying wood or charcoal, and reduce the incidence of respiratory diseases and eye problems from smoke.

Our first Seal of Approval project with A Rocha Uganda uses a design pioneered by the Centre for Affordable Water and Sanitation Technology (CAWST). These large concrete filters can provide up to 21 gallons of water per day, enough to serve a large household, with some left for their neighbors.

Once a family has been selected to receive a filter, a family member is invited to come to the A Rocha Uganda office in Kampala for two days of training in how to use it and maintain it, and then to construct their filter using locally fabricated steel molds. This helps people to understand how the filters work and builds commitment to using and caring for the filter. To use the filter, dirty water is poured through a “diffuser plate” onto a layer of sand on which a “bio-film” develops – this contains pathogens that kill bacteria. The water then trickles down through further layers of sand and gravel to remove any other impurities. We buy or source all of the parts locally, keeping construction costs low while benefiting the local economy.

Designing a project

To quantify the carbon emissions savings from providing water filters in a community, we establish what the “business as usual” or “before we started” situation is. We do this by using a baseline survey of a representative sample of the community that will be receiving the water filters.


The baseline survey is key to both the success and viability of a project. To claim emissions reductions we need to be able to prove that the introduction of a water filter will lead to households using less wood or charcoal, and consequently reducing their carbon emissions. The first question to ask, therefore, is “Are people boiling their water?”

Once we have identified households that are boiling water, it is necessary to find out how much water they are boiling and the types of fuel they are using.

We gather information on fuel usageby asking households to show how much wood they typically use in a day or week for boiling water. The surveyor uses a portable scale to weigh the fuel. The surveyor knows or comes from the community they are working in and they can “sanity check” the information.

Once we have data on household size, water consumption, and fuel usage, we estimate the average carbon emissions savings from installing a water filter. You can read our detailed methodology here. If we know the expected carbon savings over the lifetime of a filter, and the cost of construction, training, and ongoing support, we can see whether we have a viable carbon offset project.


Once families begin using the water filters, our partners carry out regular monitoring surveys to make sure that the filters are in good condition – that the filter body is not cracked, the diffuser plate is not blocked up, the biofilm layer is working correctly, and that the filter and storage containers are clean.

In addition, our partners go back and measure the fuel used in households, and compare this with the baseline scenario to ensure that households are not continuing to boil water – and that the claimed emissions reductions are being achieved.

Making a Successful Project

The most important part of any project is the people who are involved.

The households that receive a water filter need to understand the purpose of the project and to be committed to operating and maintaining the filter following the training they received.

The project partner needs to be committed to the people in the communities they are working with and able to respond to the particular demands of a carbon offsetting project.

One of the key demands is time – our carbon calculations assume that the filters will last for at least 12 years. The project partner needs to take responsibility for the project for its whole lifetime to achieve the carbon emissions savings estimated at the start of the project. To this end, we include in our budget funding for “Filter Buddies”.

Filter Buddies all have their own water filter, have demonstrated that they take good care of their filter, and are willing to help others. We provide training and a small stipend for them to act as local representatives and advisors. Each buddy is responsible for 10 households in their neighborhood that they visit regularly, providing support and encouragement to keep using the filters, and connecting with the project partner to organize necessary repairs and ongoing monitoring surveys. This ensures that the attrition rate, i.e. filters breaking or falling out of use, is as low as possible.

The project budget includes ongoing support and monitoring from Filter Buddies, minor repairs, and one renewal of the sand and gravel per filter.

The Projects

Water Filters
Fireless Cookers

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