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Potable water treatment
Potable water treatment

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2.7 Infiltration

Entry of precipitation through the soil surface and on downwards, by gravity, is known as infiltration. The rate at which this process can take place is governed by the permeability (a measure of the ease with which water can flow through the subsurface layer) and by the existing degree of saturation of the soil. Infiltration can be impeded by outcropping impermeable rocks or by paved areas, and also by the presence of finegrained soils with a low permeability (such as clay). At certain times it will be inhibited by frozen ground or saturated soil, and in Arctic areas by frozen subsoil the whole year round.

The total amount of infiltration will depend upon the rate at which it can take place, and upon the time available for water to seep into the ground. You should appreciate that rapid run-off of water will reduce the time available for infiltration and decrease the total amount taken into the ground.