Explanation of a cisterna

A cisterna is a tank for storing water and is usually constructed of brick and rendered with cement. It is light proof to stop algae forming, and the water is kept pure by chlorine tablets held in a floater. The water is usually clear and clean but is normally only used for washing and showers.

The cisterna above the house is filled by pumping water up from the swimming pool, which is filled directly from the river by a pipe coming from a communal pump house. It's not a good idea to take water from the swimming pool and disturb its balance, so in time a new cisterna next to the pool will be used to store river water to feed to the upper cisterna.