Groundwater is one of the earth’s most important natural resources. It is the water that saturates the spaces between particles of soil, sand, gravel, or rock in the subsurface of the earth. This water is stored in and moves slowly through aquifers (porous layers of rocks that can hold water). Groundwater is a major source of drinking water for humans and other animals; it is also used for irrigation, industry, and to support ecosystems.
The majority of groundwater is clean and does not require treatment before it can be used. However, because groundwater is often found in close proximity to human activity (such as agriculture, mining, or wastewater disposal), it can become contaminated with pollutants. When this happens, it may require treatment before it can be used safely.
Groundwater is replenished by precipitation that percolates (seeps) down through the soil to recharge aquifers. This process can take centuries, so it is important to use groundwater wisely to ensure that this valuable resource will be available for future generations.