EMAS cistern
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 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.
Suitable Conditions
It is suitable in areas where the land is not too rocky or weak, and it is possible to dig reasonably deep into the ground. It can be built in any climate, since temperature or other weather conditions do not affect the tank.
| Advantages | Disadvantages |
|---|---|
| - A water truck can simply let water fall into the tank by gravity – no pump is required - Water can be directly pumped into a household storage tank with an EMAS pump |
- The ground must be stable enough to dig deep into it - Cracks are harder to detect and fix (than above ground tanks) |
Resilience to changes in the environment
Drought effects on cement
Effects of drought: Badly made concrete and cracked linings (e.g. in tanks, dams, waterways, wells, and other structures).
Underlying causes of effects: Less water used for curing; Impure water used for mixing.
To increase resiliency of WASH system: Ensure adequate mixing, ratios, purity of ingredients; Minimize water content in mixture; Ensure adequate curing.
For more information on drought: Resilient WASH systems in drought-prone areas
Construction, operations and maintenance
Water can be directly pumped out of the cistern using an EMAS pump.
- Dig a large hole in the ground, with a diameter of 0.8m for the 1st meter, so that the cover does not need to be very large.
- Below that increase the diameter to 1.40-1.80m and round it off so the bottom is ballshaped. The cistern is on average 3-4m deep, but can be made deeper if necessary.
- Install the inlet pipe.
- Install a foundation of mud and stones about 30cm deep, built around the cistern, and build up about 30cm above the ground.
- Cover in mortar or cement to waterproof it.
- About 10cm above the ground, another outlet pipe is set, if the cistern becomes too full.
- Cover the walls of the cistern in mud cakes, and 2 layers of cement white wash. The walls should not be too thick or they will crack.
- Build an arch-shaped cover by lying cement on a mold of mud hill covered in plastic. The thickness of the cover depends on the diameter. A 1m wide cover should be about 5cm thick.
- Place a short guide pipe is at the centre of the cover.
- Install the EMAS pump. Its pipe is set in a larger stiff guide pipe, which reaches down to the bottom of the cistern and is fixed in place using cement.
- Cover the guide pipe with a waterproof stopper. Use a knife to perforate this with a small hole for water.
- Cover with a net to prevent insects from entering the tank.
Maintenance
The cistern needs to be cleaned regularly, particularly if it is being used for flocculation and sediments collect at the bottom. This can be done by removing the pump from the guide pipe and placing it loosely in the tank. Then all the sediments can be pumped up from the entire bottom of the tank.
Costs
Costs can be divided as such: 1/3 = cost of materials; 1/3 = cost of transport, labour, etc.; and 1/3 = cost to cover failures, or replacements.
Field Experiences
Manuals, videos, and links
VIDEO: Storage tanks - underground cistern in sandy soil. This movie shows how to make an underground cistern in very sandy soil. 19:02 minutes.
Acknowledgements
- Buchner, Wolfgang. Water for Everybody: A Selection of Appropriate Technologies to be used for Drinkable Water EMAS. EMAS Water and Basic Sanitation Mobile School. 5th edition, 2006.
