Drinking water comes from one of two sources: ground water or surface water. Ground water originates from precipitation that falls in the form of rain or snow and seeps into the ground, filling the open spaces, or pore space, within layers of sand or gravel (formations) beneath the land surface. Under the ground there is a zone of saturation where the subsurface is completely saturated with water. Layers of sand and gravel in this saturated zone are called aquifers. An aquifer is a geologic formation containing water in quantities sufficient to yield water to a well. The well pumps water to the surface where the water company treats it to ensure that it is safe to drink. It is then pumped into a storage tank and upon demand by the customer, flows through distribution pipes into the home and ultimately to the faucet. Approximately two thirds of Louisiana residents obtain their drinking water from ground water.
Surface water also originates from precipitation. The precipitation reaches the land surface and recharges rivers, lakes, wetlands, and other surface water bodies directly. Water is pumped from the water body to a treatment plant and then follows the same path as ground water on its way to the consumer.
There is a finite amount of water on earth. The water on earth is used over and over again. The water cycle, or hydrologic cycle, is the continuous movement of water from ocean to air and land and then back to the ocean in a cyclic pattern. The sun heats the earth's surface water (lakes, rivers, oceans, estuaries), which causes it to evaporate. Then the water vapor rises into the earth's atmosphere where it cools and condenses into liquid droplets. The liquid droplets combine and grow until they become too heavy and fall to earth as precipitation, recharging the surface water bodies and infiltrating into the ground, recharging the ground water.
Click below for a detailed description of the hydrologic cycle from the U.S. Geological Survey (U.S.G.S.).