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Groundwater

Beneath the surface of the earth -- from a few feet to hundreds of feet down -- water slowly seeps through the pores, cracks, and fractures of rocks, and in the spaces between sand and gravel. When these spaces are filled or saturate d with water, that water is called groundwater. If there is enough groundwater to supply a well or spring, the zone of saturation is considered an aquifer. In Arizona, most of the water that seeps into aquifers (recharge) comes from streams fed by mount ain runoff. Additional recharge occurs when crops and turf are irrigated and from stormwater and municipal discharge of treated sewage.

Typically, aquifers in central and southern Arizona are made of sands and gravels and yield considerable groundwater. Northern Arizona aquifers are characterized by fractured rock; in many places, wells must be drilled to great depths, and may yield little or no water.

To tap groundwater, a well must be drilled deep enough to penetrate the water table, which is the surface of the zone of saturation. When pumping occurs, the water table near the well drops, creating a cone of depression. If more water is pumped fro m an aquifer than is recharged, overdraft occurs and the water table drops. In parts of Arizona overdraft is a serious problem that has lead to land settling and cracking (subsidence), lower well yields, quality degradation and the drying up of streams a nd rivers. In 1980 the Arizona legislature passed the Groundwater Management Act to regulate pumping in areas with substantial overdraft and to bring pumping and recharge into balance.

Although the state's groundwater supply is large, it accumulated over thousands of years. Much of it is low quality or cannot easily be pumped. Efforts are underway to artificially recharge aquifers to store water for future use and reduce overdraft .

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