Somalia

In Somalia, dams are built to trap sand. Then the sand stores water.

When the rains come, water rushes through otherwise dry riverbeds. A low wall slows the flow. The heavier sand settles and builds up behind it, while finer material and most of the water continue downstream.

After several rains, a thick layer of sand has formed. Water remains between the grains, below the surface where it is protected from sun and evaporation. The sand also helps filter the water, and with no open water left standing, mosquitoes have fewer places to breed.

When the dry season comes, people dig wells down into the sand and bring the water back up.