__NOTOC__{{Language-box|english_link= Natural or artificial ground catchment and Lined sub-surface tanks | french_link= Coming soon | spanish_link= Coming soon | hindi_link= Coming soon | malayalam_link= Coming soon | tamil_link= Coming soon | swahili_link=coming soon | korean_link= Coming soon | chinese_link=天然或人工地表集水区和衬砌式地下贮水池 | indonesian_link= Coming soon | japanese_link= Coming soon }} [[Image:ground ctch icon.png|right|80px]]
[[Image:MasonryTank.jpg|thumb|right|200px|Stone masonry round berked under construction showing wires for roofing materials. Somaliland. <br>Photo: Eric Fewster, BushProof / Caritas.]]
These are natural, artificial or modified catchments that have low to relatively high runoff coefficients. Water from these catchments is captured and stored in lined sub-surface reservoirs excavated below ground level. The reservoirs are known by different names (''berkeds'' in Somaliland, ''taankas'' in India, hemispherical sub-surface tanks in Kenya – also included in this category are excavated water cellars such as the ''shuijiao'' in China) and have been lined with many different materials. These tanks normally have a larger depth to surface ratio compared to open ponds and their scale means a roof of some description is a possibility. When the lining is constructed well, there will be no leakage, and water will either evaporate or be abstracted. These tanks are often privately-owned by one or more families, but can be communal.
===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.
===Resilience to changes in the environment===
====Drought====
'''Effects of drought''': Water storage used up.<br>
More information on managing drought: [[Resilient WASH systems in drought-prone areas]].
===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.
* Support the capacity of the government or private sector to be able to provide (for payment) a tankering scheme to fill tanks during the driest parts of the year.
===Costs===
Access to finance is a main obstacle to promotion of rainwater harvesting for households, and is important so that users can replicate the technology – there are few examples on a global level with micro-credit for rainwater harvesting. The cost of underground tanks can be high and variable in cost per m3 of storage (averages around US$30-40 per m3 of storage or more depending). Sub-surface hemispherical tanks made from stone masonry and bricks/cement in Ethiopia costs 113 - 219 Euro per m3 of storage including all costs. May need to pay for trucked water for construction and for a higher solidity of tanks (in clay areas). However there are several ways to save money.
* However, care needs to be taken with cheap linings – in some areas with swelling clay and differential settlement, linings can easily crack, as has often been observed in some areas. The areas where cheap linings might work therefore may be site-specific, and depend on the clay content of the soil. For plastic linings, experience from India shows that these can be punctured by rodents, crabs or insects if there is no rodent/insect-proof layer before the plastic.
===Manuals, videos, and links===
* [http://www.unep.or.jp/ietc/publications/techpublications/techpub-8a/sand.asp Sand Abstraction]. Sourcebook of Alternative Technologies for Freshwater Augumentation in Africa. United Nations Environment Programme.
* [http://www.ijest.info/docs/IJEST11-03-01-093.pdf Evaluation of the Sand Abstraction Systems for Rural Water Supply: the case of Lupane District, Zimbabwe]. Vol 3, No. 1, January 2011.
===Acknowledgements===
* CARE Nederland, Desk Study: [[Resilient WASH systems in drought-prone areas]]. October 2010.