Aquifers are critically important in human habitation and agriculture and are one of the most important natural resources of a nation. Deep aquifers in arid areas have long been water sources for irrigation. Groundwater, which is in aquifers below the surface is the main source for fresh water for human use. Aquifers also help prevent surface bodies of water from flooding: when it rains heavily, as aquifers beneath rivers soak up the excess water, preventing the surface flow from rising too rapidly and overflowing onto neighbouring fields and towns

An aquifer is a layer of sand, gravel, soil, or rock that is saturated, meaning all pore spaces are filled with water, and able to transmit groundwater in sufficient quantities for uses such as drinking water and irrigation. Groundwater does not continually dilute contaminants that reach it. Flushing a plume of contamination from groundwater may take many years. Hence, there is very little, if any, breakdown of pesticides once they reach an aquifer. When aquifers are relied upon as a source of drinking water, any pesticide contamination can be devastating.

After entering an aquifer, water moves slowly toward lower lying places and eventually is discharged from the aquifer from springs, seeps into streams, or is withdrawn from the ground by wells.

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