Local Water Utilities United for Safe Drinking Water

What is Groundwater?

How does groundwater get in the earth? Where does it come from?


The Hydrologic Cycle

Groundwater begins as rain or snow that falls to the ground. This is called precipitation. Only a small portion of this precipitation will become groundwater. Most will run off the land surface to become part of a stream, lake or other body of water. This water we call “surface water.” Some of the water is used by plants and returned to the atmosphere. This is called transpiration. Some of the water evaporates off the land to become water vapor once again.

The remaining precipitation seeps, or percolates into the earth to become “groundwater.” These actions make up the Hydrologic Cycle. Water is in a constant cycle of change, from one form to another. From liquid to vapor to ice or snow and back to a liquid state.This same water from rain or snow continues down through the soil until it reaches an area that is saturated with water, and is called the “saturated zone.” Water in this saturated zone is called “groundwater”.

The point where water reaches the saturated zone is called the “water table”—because it is like a table top. Above is the unsaturated zone full of rocks, soil and earth that have let water seep down. Below is the saturated zone of groundwater. The saturated zone below the water table has water that fills the spaces (or pores) between rock particles or the cracks (fractures) of the rocks. This is where groundwater is found. This is where groundwater that you drink, bathe or use for daily chores comes from. We call this geologic area of groundwater an AQUIFER.

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