[[Image:RechargePit.jpg|thumb|right|300px|Recharge pit constructed for recharge of surface runoff. Rajasthan, India]]
Large diameter wells and smaller diameter boreholes can be used to directly recharge or dilute shallow aquifers where low permeability strata (rock) overlie 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. Wells that have run dry due to falling water tables from over-exploitation are also increasingly being used for this purpose. Recharge wells are also advantageous when land is scarce. Water can be injected into a well or borehole and recovered from another some distance from the first, to increase travel time and benefit from the water treatment capacity of the aquifer. This is referred to Aquifer Storage Transfer and Recovery (ASTR). In loosely consolidated material, recharge pits and trenches are also used in cases where low permeability material overlies the aquifer, which occurs at trench-able depth, approximately 5-15m. Structures are excavated sufficiently deep to penetrate the low permeability strata, in order to provide direct access to the aquifer. Trenches or pits can be build to maximise the side-wall surface area and minimise the bottom surface area in order to facilitate horizontal movement of recharge water into the aquifer. The facilities should ideally be covered to keep out sunlight, animals, and people.
==Suitable conditions==
* Site only in areas where rainwater does not infiltrate fast enough where there is high runoff.
* '''Avoid''' where there is a risk of chemical contaminants entering the well, e.g. fertilizers and pesticides from agriculture, and when the final
water abstracted will be used for drinking, unless you have the ability to apply an appropriate filter.
==Construction, operations and maintenance==
[[Image:RoofToAquifer.jpg|thumb|right|400px|Roof to aquifer recharge. Unicef / Ara Centro. (2009)]]
====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 overexploitationover-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.
One source of higher quality water that is a realistic source of recharge water is rainwater from roof catchments. This has been used to recharge shallow aquifers in Mozambique where groundwater was saline, with the result that the water was diluted. Ground runoff is also being used where potentially contaminated runoff water is used to recharge aquifers but where it still must infiltrate a certain amount of soil later – however the risk of aquifer contamination and screen blockage is increased. Hand dug wells that previously dried up now have water all year round – an evaluation after 3 years showed that out of 120 hand-dug wells that had recharge boreholes created close by to aid recharge, very few were drying up like they were before. In addition, families in the area were starting to replicate the system on their own.
5) Cleaning involves swabbing the inside of the PVC with a cloth.
* Sand filters can also be used instead of the PVC filter system – this is where sand replaces the need for a cover piece and the need to wait 4 hours. It can be used with rooftop catchments where no surface runoff enters the hole, and could be done with or without a PVC pipe.
====Maintenance====
Some chemical pretreatment of the water may be required to prevent flocculation of iron, CaCO3, etc. and chlorination of other disinfection may be needed to prevent microbial growth. Clogged wells may need to be recovered at regular intervals using surging and pumping to remove fines and bacterial growth physically and the use of a wetting agent to remove air in an air-clogged well. Carbonate aquifers exhibit the least amount of clogging due to the gradual dissolution of calcite by a slightly acidic injectant, if periodic backflushing is observed.
==Costs==
