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==Suitable conditions==
* Site in a place where run-off is seen to flow after rains.
* Artificial catchments are created where infiltration of runoff zone is high.
- Microbiological and chemical water quality is likely to not be acceptable for direct consumption
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==Resilience to changes in the environment==
====Drought====
'''Effects of drought''': Water storage used up.
'''Underlying causes of effects''': Lack of rainfall; High evaporation rates; Leaking linings due to bad construction; Storage not sufficient for demand – tanks are too expensive for volumes of water to outlast extended dry periods.
'''To increase resiliency of WASH system''': Build smaller tank structures but more of them over longer time, which means less reinforcement per tank, more manageable to construct and cover, and more affordable; Reduce evaporation & seepage due to poor construction & siting; Follow proper concreting guidelines; Make tanks from cheaper materials and repair more often; Improve access to micro-finance; Support the capacity of the government or private sector to be able to provide (for payment) a tankering scheme.
==Construction, operations and maintenance==
'''General advice on cement''': A common cause of cracks in structures and linings (e.g. in tanks, dams, waterways, wells) is errors in mixing and applying the cement. First of all, it is important that only pure ingredients are used: clean water, clean sand, clean rocks. The materials have to be mixed very thoroughly. Secondly, the amount of water during mixing needs to minimal: the concrete or cement needs to be just workable, on the dry side even, and not fluid. Thirdly, it is essential that during curing the cement or concrete is kept moist at all times, for at least a week. Structures should be covered with plastic, large leaves or other materials during the curing period, and kept wet regularly.
'''Specific advice''':
The reason for constructing a sub-surface tank is to store the water. Therefore one of the most important aspects is that seepage and cracks must be avoided. Therefore good quality construction work with adequate supervision is vital to create a sound structure – this is especially important in areas with swelling soils that can affect the integrity of the lining. While ownership and management of tanks is important, such privately-owned tanks have often failed due just to the technical construction component. Construction materials vary and include the natural soil formation itself, clay, stone masonry, bricks/cement, ferrocement, anthill/lime/cement and plastic/rubber lining. Material may affect cost but choice may also depend on what is available and the type of surrounding soil. To generally prevent cracking/seepage:
* Round tanks are inherently stronger than rectangular ones. Hemispherical and cylindrical designs are commonly used.