A hole which has been dug, bored, driven or drilled into the ground for the purpose of extracting water is a well. A well is considered to be shallow if it is less than 50 feet deep. The source of a well is an aquifer. Aquifers are replenished as rainfall seeps down through the soil.
Ground water travels through permeable soil on top of hard or impermeable layers.
The level at which the soil is saturated is the water table. Pumping the well lowers the water table near it. These wells are particularly sensitive to seasonal changes and may dwindle during dry periods. Artesian wells penetrate into ground water having confining layers above and below the aquifer. Rainfall enters into the aquifer through permeable layers at high elevations causing the ground water to be under pressure at lower elevations.