Sand and Gravel

Crushed rock makes the best sand and gravel for filter construction and can be obtained from gravel pits or quarries. When crushed rock is not available, sand from a quarry or pit, or sand and gravel from river banks can be used instead with some added cleaning. Various sized sieves sort the gravel and sand used to build the concrete container and are used inside as filtration sand. When everything is sorted it is washed.

Concrete Container

Teams build molds that are used to form the concrete container. Molds are assembled and a piece of tubing is run from the bottom of the mold to the spout. Sand, gravel, cement, and water are mixed together to make the concrete mix. It is tested to ensure it is not too dry or wet, then into the mold and left to rest for 24 hours. When the mold is removed, the filter is filled with water and left to cure for 7 days.

Diffuser and Lid

1) Diffuser: The diffuser plate protects the biolayer when pouring water into the filter, helping the water drip evenly across the sand maximizing water filtration. It is made from local materials, normally wood or tin, and is crafted by local craftspeople. Holes 3 mm in diameter are spaced out by 2.5 cm in a grid pattern.

6) Lid: The lid prevents anything from getting inside the filter. It can be made out of several materials, usually tin or wood locally sourced, and made by local craftspeople with the skills to work with the material. 

Install Filter

The concrete container is transported to the customer’s home with the components that will go into it. About 10 litres of water and a small amount of laundry bleach is added to disinfect everything, is poured into the filter which will help prevent air pockets and dry spots as sand and gravel is added. From there 3 litres of gravel is added to form a drainage layer. Then 3.25 litres of separation gravel is added, 30 litres of filtration sand is added to the fill line. The diffuser plate is installed and additional water is poured into flush out the bleach. Finally flow rate is measured to make sure it operates correctly.