[[Image:InfiltrationWell.JPG|thumb|right|250px|Infiltration well in Madagascar. Eric Fewster, BushProof.]]
Also called interception wells, these are shallow wells which draw water from a natural aquifer outside of a riverbed, but which have a partial lining. They are useful where recharge of the aquifer is low due to low rock/soil permeability. Unlike inlet wells and drainage wells, however, infiltration Infiltration wells do not have to have a direct water inlet at ground level: rather, they . They can form a larger hole and be filled with porous natural materials to increase the ground's infiltration capacity through the installation of porous materials and, in most cases, have a coiled drain between the soil surface and the underground piping. Rocks, coarse wood chips or straw can be used as filtering material. Wells made of straw are constructed like permeable trenches and do not have a coiled drain, which can limit their infiltration capacity.
==Suitable conditions==
* Site where water table is within 5 metres of ground surface, and where soils are stable.
* Site where water demand is low, e.g. for small communities.
* Do not install in areas where water drainage is rapid. Since infiltration wells have a low infiltration capacity, the drainage rate will be insufficient and will not make it possible to reduce the risk of erosion.
====Avoid contamination====
# A pump can then be installed within the intake screen.
* Where wells dry up in the dry season, recharge techniques could be used upstream of the well.
====Rock or wood chip infiltration wells====
[[Image:WoodChipInfiltrationWell.jpg|thumb|right|300px|Infiltration well filled with rock or wood chips - soil not tilled.]]
A hole measuring 1 to 1.5 m in diameter and approximately 1 m deep is excavated at the location selected for the infiltration well.
If the well is constructed with rock in sandy or loamy soil, the bottom and sides of the excavation can be covered with a geotextile membrane (of the Texel 7609 or 7612 type). This membrane will prevent lateral clogging by the rock and is attached to the drain with drainage adhesive tape where the drain crosses it. The membrane is cut 30 cm below the surface of the soil if the soil is to be tilled above the well once installation is complete. Otherwise, the membrane can extend up to the soil surface. Note that no geotextile membrane is used in wood-chip wells.
The excavation is progressively backfilled with the desired material. The drain is coiled in the porous material as it is placed in the hole. In wells made of rock, it is recommended that backfilling begin with clean 56-mm rock, although finer stone (such as 19-mm stone) can also be used.
The drain is cut at the desired height, and a cap is placed at the end. If the soil is to be tilled above the wells after the work is complete, the coiled piping must stop at least 30 cm below the ground surface so that the piping is not damaged by tilling equipment. The backfilling of the rock well is completed with materials that will not damage the tilling equipment (coarse soil if available, coarse sand, wood chips or clean 19-mm stone). Laying a geotextile membrane between these two zones is not recommended, because it would quickly be clogged by the silt contained in the surface runoff. Wood-chip wells are generally fully backfilled with wood chips.
Where the erosion rate is high and the risk of clogging is significant, it is preferable that the soil above the infiltration well not be tilled. A minimum radius of 3 m around the well is therefore grassed over to filter the soil particles and create a buffer zone between the tilled soil and the infiltration well. The well can also be covered with rock (e.g. clean 100- mm rock) to finalize the installation.
====Maintenance====
Generally, it is recommended that minimum tillage practices be adopted to maximize the lifespan of the well. If a well gets clogged, the first 30 cm of the porous material is replaced to improve the infiltration capacity.
Organic filtering materials decompose gradually over time. Because of better oxygenation conditions near the ground surface, decomposition is faster in the upper part of the well. In wood-chip wells, it is generally necessary to add more wood chips every 10 years to compensate for subsidence caused by the decomposition of the material in place. Given its lower carbon/nitrogen ratio and high cellulose content, straw decomposes much faster and must be replaced more frequently. Coarse sand can also be used to replace decomposed material in both cases.
Lastly, infiltration wells and separate drain outlets must be inspected frequently to evaluate the condition of the structures as well as their efficiency in improving surface drainage and reducing erosion problems.
==Costs==
