[[Image:EMAS cistern icon.png|right|80px]]
[[Image:Building a vertical cistern.jpg|thumb|right|200px|Building a vertical cistern]]
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EMAS Cisterns are underground tanks coated with a thin layer of cement mortar and made waterproof with a pure cement whitewash. It is common for 2-3 cisterns to be constructed per household, particularly when rainwater is the main water source, for a total of 4000-8000 litres of space. An EMAS pump can be installed to pump water from the cistern to local faucets in the house.
The cistern can also be used as a reserve water supply, if the water supply from neighborhood wells is irregular or only available during the rainy season. This is also useful if the regular water supply is suitable for washing, etc. but too salty or polluted for drinking. It can also be used to store treated sewage water until it can be used for irrigation. It can further be used as a treatment tank for example for flocculation of turbid water.
The general design is for a vertical cistern, though there are variations, such as the [[Horizontal Cistern cistern | Horizontal Cistern cistern ]] suitable for different conditions.
EMAS is the acronym for Escuela Móvil de Agua y Saneamiento (Mobile School for Water and Sanitation), in Bolivia, whose director, Wolfgang Eloy Buchner, developed the EMAS pump in the 1990s. EMAS is not only the name of the mobile school for water and sanitation, but also a whole technical and social concept of water and sanitation which includes rain water harvesting, solar water heaters, windpower, hydraulic rams, water treatment, small tanks and sinks, a variety of hand and foot pumps, and ferrocement tanks. The aim of the technologies and systems is to achieve the necessary supply of drinkable water, and water for micro irrigation in rural and sub urban areas.