When a person opens a spigot to draw a glass of water, he or she may be tapping a source close to home or hundreds of miles away. This web page is intended to help Californians identify their source(s) of drinking water, learn more about how drinking water is treated, and learn how to help prevent pollution of our groundwater and surface water supplies.
Use the links at left to learn where water comes from to supply various parts of California.
Development of this webpage was funded by a Proposition 50 California Bay-Delta Authority Drinking Water Grant administered through the State Water Resources Control Board. Special thanks to EIP Associates for providing the GIS data for the cities.
This site lists the drinking water source for incorporated cities with a population of 10,000 or greater. Data sources: 2005 Water Education Foundation survey, water agencies, and annual water quality reports.
Funded by Proposition 50. CALFED administered through SWRCB. Special thanks to EIP for GIS data.
Water is essential for life as we know it. Water grows our food,
powers turbines for electricity and serves as the lifeblood of
industry. Water nurtures our landscapes and provides habitat for
wildlife. It is estimated between 70 and 75 percent of the
Earth’s surface is covered with water, more than 96 percent of
which is too salty for most human uses.
Today, significant technological developments in monitoring,
assessing and treating water ensure a drinking water supply of
high quality for most people.
Water is continually moving around, through and above the Earth.
It moves as water vapor, liquid water and ice. It is constantly
changing its form. The movement of water is referred to as the
hydrologic or water cycle. Precipitation,
evaporation/transpiration and runoff (surface runoff and
subsurface infiltration) are the primary phases in the cycle.
Surface water refers to water that remains on the earth’s
surface, in rivers, streams, lakes, reservoirs or oceans.
Public agencies and private water developers have built nearly
1,400 reservoirs in California to capture seasonal runoff,
protect against floods and allocate water supplies throughout the
year. These reservoirs hold about 42 million acre-feet of water
Nearly a century ago, controlling water-borne disease was the
main treatment goal of water providers. Today, water agencies
large and small provide their customers with the highest quality
drinking water in the world. Before disinfection became a common
practice, widespread outbreaks of cholera and typhoid were
frequent throughout the United States. These diseases are still
common in less developed countries, but largely disappeared in
the United States when chlorine and filtration became widely used
80 years ago.
When water is provided by a private well, periodic testing of its
water is recommended but not mandated. Owners of private wells
should use only laboratories certified by the California
Department of Heath Services to conduct an analysis. Private
wells fall outside federal and state regulation because they are
on private land and not covered by the SDWA. They also are not
subject to the same periodic testing and monitoring requirements
as public water systems. There are more than 600,000 private
wells in California.
In California, the Department of Health Services (DHS) is
responsible for regulating drinking water and for monitoring
approximately 7,500 public water systems to assure the delivery
of safe drinking water to all Californians. For small systems
with 200 or fewer connections, the DHS’ Drinking Water Field
Operations Branches (DWFOB) work with county health departments,
planning departments, and boards of supervisors that have primary
Many small systems are located in low-income communities, making
it more difficult to raise funds for improvement.
Pollution that impacts water quality is divided into point and
nonpoint sources. Point source pollution is discharged from a
known source, such as a wastewater treatment plant or a factory.
Point sources are monitored and regulated to control discharges.
The leading cause of water quality problems is nonpoint source
pollution, the accumulation of runoff from city streets,
construction sites and agricultural fields, spills and abandoned
Even as the available supply of water in California remains
fixed, the state’s increasing demand means water suppliers and
water users must do all they can to squeeze the most use from
each precious drop of water. This necessity becomes even more
evident in years when drought conditions exist and the water
supply is precariously balanced between urban, agricultural and
Water conservation is an essential tool to stretch the water
supply – or more accurately, to use the existing supply more
Conjunctive use is the coordinated management of surface water
and groundwater supplies to maximize the yield of the overall
water resource. An active form of conjunctive use utilizes
artificial recharge, where surface water is intentionally
percolated or injected into aquifers for later use. A passive
method is to simply rely on surface water in wet years and use
groundwater in dry years. More than 65 water agencies in the
state operate groundwater recharge programs. The success of many
of these programs, however, depends on purchasing available
surface water from other users.
The process of removing dissolved minerals, such as salt, from
sea water and brackish groundwater is gaining favor as a method
of augmenting urban water supplies. Estimates are that seawater
and brackish water desalination will increase by 10 to 20 percent
in the next decade, with existing and envisioned operations
eventually generating an estimated 700 million gallons per day.
About two dozen seawater desalination plants are proposed along
the California coast.
Estimates are that seawater and brackish water desalination will
increase by 10 to 20 percent in the next decade.
Water recycling (or water reclamation) involves treating
municipal wastewater to remove sediments and impurities for
reuse. As demand for water increases, techniques for recycling
and reuse of water become more attractive. Using recycled water
reduces reliance on increasingly scarce and expensive surface
water and can minimize groundwater overdraft (extracting more
water than is replenished.) Additionally, as a direct result of
water recycling, discharges of treated wastewater into rivers and
the ocean are reduced.
Although water seems limitless and is for the most part taken for
granted, it is not an absolute certainty that where settlement
occurs, water will follow. This fact has not escaped water
experts and decision-makers, who realize the many competing needs
for a precious resource that has no substitute.
As California heads toward a future of further population growth,
a number of factors have to be considered as agencies look to
accommodate the increasing demand.