Where Drinking Water Comes From

Overview of Surface Water and Groundwater

At a high level, drinking water comes from both surface water and groundwater sources. It is important to know which source your drinking water comes from because different laws and regulations apply to their management, treatment, and long-term sustainability. Generally, drinking water laws are in the Corporations Code, Education Code, Food and Agricultural Code, Government Code, Health and Safety Code, Public Resources Code, and Water Code, and drinking water regulations are in the Code of Regulations.1

To learn more about your drinking water, the water system that provides your drinking water, and the drinking water contaminants that affect you, visit Community Water Center’s Drinking Water Tool.

Drinking Water Tool

Surface Water

  • Surface water is freshwater from lakes, rivers, streams, and other water bodies that are open to the air.2

  • Surface water, due to being directly exposed to the air and any activities that occur on land, is more easily contaminated and has specific treatment requirements before it can be used as drinking water.3

  • Surface water is regulated by the State Water Board, through laws as part of the California Water Code and Health and Safety Code, and regulations as part of the California Code of Regulations.4

Groundwater

  • Groundwater is water that exists under the surface of the land - water that has gathered for thousands of years under our feet to create an underground “aquifer”. Aquifers are like big underground pools, but with rocks and soil scattered throughout them. 

  • Groundwater is usually provided through three different water systems: a private, domestic well; a small, state water system; or a public water system. In other words, one of these three systems gets the water from the aquifer underground to you, the consumer. 

    Learn more about these systems: (English/ Español)

  • About 85% of people in California rely on groundwater for all or part of their drinking water supply.5 Further, groundwater is the main source of drinking water for communities in the Central Valley and Central Coast. In recent decades, groundwater levels have dropped due to overdraft Overdraft is when too much water is taken out of the ground without enough water going back in to replace what is used. Overdraft is a common, severe concern where industrial agriculture uses up a lot of groundwater or when drought conditions result in little to no rain that can replace water used from aquifers. 

    Learn more about groundwater regulation, contamination, issues with using groundwater, and groundwater advocacy (English/ Español).

This Page Last Updated: June 13, 2024