====Save on costs====
High cost of tank construction will decrease water availability because smaller tanks can be made. Ways to increase storage are to build with cheaper lower quality materials, use less material for construction and reduce labour costs. In this way, sub-surface tanks can become a more realistic option. Ideas include:
* Use existing soil as a natural lining if it is relatively impermeable. In China, clay has been used to line excavated water cellars (called Shuijiao) in areas where the natural soil (loess) is already fairly impermeable. The lining process is difficult and time-consuming and has been replaced largely by ferrocement or plastic. However, it proves that in some areas it is possible to construct a low-cost tank. In Somaliland, similar water cellars were observed that were excavated in impermeable stable soil formations – runoff water entered through a small inlet channel. Other tanks are sealed with a 10cm unreinforced cement lining – it seems that 30m3 is the most economical size = , as it is the most volume without needing reinforcement – such tanks cost US$189 or about US$6.3 per m3 of storage (materials only presumably).* In Kenya, tank linings have been made with powdered anthill material and lime which substitute some of the cement and bricks, bringing cost to US$9.8 per m3 of storage.
* Reducing the size of structures. More manageable to construct in terms of cash flow, and easier to cover. This way, tanks are more affordable to families, and more tanks can be added in subsequent years, thus spreading out costs.
* 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.