Metropolitan Water District of Southern California
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About 65 percent of all the precipitation in California soaks into the ground, evaporates or nurtures trees and plants. The rest is surface runoff that flows into rivers, streams and lakes.

Most water supplies in Southern California begin as snowmelt or rainfall that flows into rivers. However, most of that precipitation—75 percent—occurs in the north, while the majority of people live in the south. To alleviate the imbalance, water is imported from one end of the state to the other through aqueducts that are several hundred miles long. Both federal and state rules protect the drinking water along its journey.

Several agencies keep an eye on water, even before it reaches a treatment plant. These include the U.S. Environmental Protection Agency (EPA), State Water Resources Control Board, California Department of Health Services (DHS) and of course, Metropolitan Water District of Southern California.

That raw or untreated water goes through several steps before it is ready to make its way through the pipes and into a home or business. First, the water flows through screens, which filter out leaves, sticks, fish and other large debris. This can be done at a treatment plant or before it gets there. Once the water is filtered (screened), it gets a shot of chlorine to disinfect it and to help control taste and odor. Coagulants are added to the water to cause very fine particles to clump together into larger particles. Flocculation is a high energy mixing of the water that—just like using a blender to make a fruit smoothie—combines the particles. The water is then slowed down so the large particles formed in flocculation process settle out. The filters provide for removal of remaining particles and impurities from the water. The water then gets another dose of chlorine, to kill any leftover disease causing organisms and to give it a little extra protection for its next journey—to a reservoir. Before entering the reservoir ammonia is added to form chloramines.

Chloramines are disinfectants used to treat drinking water.  Chloramines have been used by water utilities for almost 90 years, and their use is closely regulated.  Metropolitan uses chloramines in its water pursuant to a permit issued by the California Department of Public Health.  More information regarding chloramines can be found on the United States Environmental Protection Agency’s website.

The time it takes to treat water varies widely, depending on the temperature of the water, its pH and what’s in the raw water. In the winter, for example, water is colder so it requires a longer exposure to chlorine to be properly disinfected.

When Metropolitan sells the water from its reservoirs to a local water agency, the water quality is still monitored by EPA and DHS. These agencies have strict rules that require water providers to test for more than 100 different contaminants and to share their findings with consumers in an annual report.

Once the water enters the plumbing lines of your home or business, your water utility and the health agencies no longer protect its quality. The reason is that they can’t control factors like old and rusted pipes and faucets. This is when you take over some responsibility for the quality of your drinking water.

Once inside the home, the water has myriad uses, from human consumption to washing clothes and irrigating lawns. The average family of four uses about 163,000 gallons of water—about 2,608,000 glassfuls—a year for all its water uses in and around the house.

Page updated: June 13, 2013