Lots of people use groundwater. It is used in industry, for drinking at home and to water crops. When the rain or snow falls from the sky, it gets the ground wet.
Gravity pulls the water through the dirt.
The dirt then filters out some of the pollution. This is called the Saturated zone. On top of the saturated zone is the water table. The water table can be a few inches from the surface or be hundreds of feet below the ground. The water in lakes and rivers is called surface water.