Underground tank
Where access to groundwater is limited, rainwater harvesting in underground tanks can be an effective and low-cost alternative. Water stored in the wet season can be used in the dry season and lifted from the tank with a rope pump or with a deep well pump, which can elevate water up to 30 m.
These tanks can be constructed of concrete blocks. The tanks are partly (1.5 m) build below the soil surface. These tanks can store up to 20 000 liters of water, used for domestic use, cultivation.
History and social context
The Brazilian government, with support from organisations such as UNICEF and IRCSA (International Rainwater Catchment Systems Association) started a programme to construct one million rainwater tanks in Brazil.
With regard to the concrete block tanks, 40 community water tanks (supporting a few families each) were implemented successfully. Following this success, another 80 concrete block tanks will be build at household level.
Practica foundation is testing various options for low-cost storage and groundwater recharge like the "Reed cement tank" and the "Tube recharge".
Suitable conditions
The area should be suitable for rainwater harvesting. Depending on the design the capacity of the tank varies from 3 500 to 20 000 liters.
| Advantages | Disadvantages/limitations |
|---|---|
| - Low cost alternative to metal or ferro-cement tanks. |
Technical specification
Operation
Basic water quality testing is recommended during the first year, with further testing when water quality is in doubt. Eg. the 'HACH' pillo test, costing about US$ 1 per test. Treatment to manage microbiological quality is also recommended.
Maintenance
- Removal of debris and overhanging vegetation from gutters and the roof (preventing stagnation of water in the gutters) is required. Physical inspection and repairing cracks with cement is also needed.
Manufacturing
Material costs for EMAS tanks consist of sand and four 50 kg bags of cement for each tank.
Estimated Lifespan
Cost
Subsurface ferro-cement tanks of 60 m3 costs about US$ 1 900.
Country experiences
Manuals
This Underground tank installation Manual by Tankmasta explains all the steps needed to build an underground tank.
Movies
External Links
- General www.rainwaterharvesting.org www.unep.or.jp www.rainfoundation.org
- Recharge www.practicafoundation.nl
- Storage www.emas-international.de
Footnotes