Changes

Large diameter wells and smaller diameter boreholes can be used to directly recharge or dilute shallow aquifers where low permeability strata (rock) overlies the aquifers and where other infiltration methods are not effective. The important thing is that water of high enough water quality is used for this purpose. Although this method of recharge is practised with deep and high-yielding boreholes, this technique mainly describes recharge at the family level in areas where hand dug wells run dry at the end of the dry season or where groundwater is saline.

==Construction, operations and maintenance==

====Water source considerations====

Water to be recharged should be high quality since blockage due to suspended sediment, microbial growth or chemical precipitation is more likely over the smaller infiltration area of a well or borehole. In Namibia, water from the water treatment works is further treated with granular activated carbon and chlorination before being injected to avoid such problems. In certain cases in India, open large diameter wells that ran dry due to falling water tables (resulting from over-exploitation) are being used to recharge shallow aquifers directly from runoff water that enters the wells – the problem with such structures is that there is no process of water infiltrating through the soil to the aquifer, which would not only reduce sediment and microbiological load, but also have potential chemical contaminants like nitrates and pesticides. Direct recharge of untreated water via open wells is therefore discouraged in preference to infiltration through a soil or sand layer. However, since silt and contaminants can more easily enter through a well, course gravel is sometimes filled into it to act as a filter, which can be replaced if clogging becomes severe.