Water enters soil naturally through precipitation. This percolating water, called recharge, passes downward through the root zone until it reaches the water table. Immediately below the water table lies the saturated zone. In this zone, all pore spaces are filled with water. Underground layers of sand, gravel, or permeable rock that contain enough water to serve as a water source are called aquifers.
Aquifers vary greatly in size.
Smaller ones may supply only a few wells. Some aquifers are large enough to supply water to thousands of households and business. Groundwater can become contaminated from the chemical fertilizers and pesticides which we use on our lawns and gardens. As recharge water percolates through the soil, it can carry these chemicals downward to the water table. Once in the saturated zone, these pollutants move with the groundwater, forming a region of contaminated water called a plume.