Drinking water treatment and distribution

Drinking water treatment is among the most important public health achievements of the 20th century.  However, agencies responsible for drinking water treatment and distribution face major challenges related to emerging contaminants, infrastructure, and the quality of source water.

Toolbox Main Page IconMany people count the widespread treatment of drinking water among the most important public health achievements of the 20th century. However, agencies responsible for drinking water treatment and distribution face major challenges related to emerging contaminants, infrastructure, and the quality of source water.

Breakthroughs in health science and advances in technology to detect contaminants at trace levels have shifted the focus of water treatment beyond filtration and disinfection to a multi-barrier approach that starts with protecting water at the source and includes actions at every point in the water distribution process. The emphasis today stretches beyond providing safe drinking water to also ensuring the disposal of wastewater in a sustainable way while finding ways to protect lakes, rivers, groundwater, and other sources of water.

Water treatment and distribution in California is an important undertaking with many people who depend on it. In California, 93 percent of residents rely on public systems for water to use for drinking, cooking, and bathing. Just seven percent of the state’s residents have their own well or private water supply. Public water systems in the state share the goal of providing a reliable supply of safe drinking water to those it serves. This means treating the water as well as distributing it. A wide range of people and places depend on these systems, including cities, homes, schools, hospitals, campgrounds, parks, and gas stations.


In California, the State Water Board’s Division of Drinking Water develops and enforces drinking water regulations, and these regulations apply to all public water systems. It doesn’t matter if they are privately owned by investor-owned utilities or mobile home parks; or publicly owned by municipalities or the state.

However, privately owned and for-profit water systems are regulated by the California Public Utilities Commission for the purposes of establishing water rates, though there are some exemptions. One exemption is for systems owned by homeowners’ associations or shareholders who only provide water to their shareholders or members; another exemption is for privately owned mobile home parks, though the CPUC may investigate water rate abuses if they receive complaints.

While the state has the primary responsibility for administering and enforcing these regulations, the U.S. Environmental Protection Agency coordinates with state and local agencies on the implementation of the federal Safe Drinking Water Act. The EPA also directly provides regulatory oversight for tribal water systems.


Treatment processes disinfect, blend, and filter water from lakes, rivers and underneath the ground in an effort to bring raw water into compliance with state and federal drinking water standards. A wide range of facilities – some 8,560 facilities statewide – treat surface water and groundwater, using processes such as chlorine disinfection, sedimentation basins, filtration, membrane filtration, ultraviolet light, ozonation, chemical removal, and blending. In California, adding fluoride to the water is a common practice to accrue dental health benefits, and a list of water systems doing so is kept by the State Water Resources Control Board.

Some of the treatment processes listed above have been around for many years, and others are new and innovative treatment technologies developed to meet new and more stringent drinking water standards, improve efficiency and reduce waste. Newer technologies gaining traction in California thanks to how they help meet new regulations are:

Both the EPA and the State Water Board’s Division of Drinking Water examine new and existing health risks from constituents found in drinking water. Regulations include established requirements for quality monitoring, maximum contaminant levels (MCLs) in the water delivered to customers, multi-barrier treatment, and more.

Among the emerging contaminants that have some scientists and consumers concerned are pharmaceuticals and personal care products, or PPCPs. These contaminants include ingredients in prescription and nonprescription medicines, cosmetics and other products. PPCPs have been detected in groundwater, streams, rivers, lakes, and reservoirs in the U.S. at very low concentrations, and have commonly been detected in combinations of chemicals. Typical drinking water and wastewater treatment systems were not designed to remove PPCPs from water. However, some of the conventional treatment processes do reduce the concentrations of PPCPs in water to an extent. The American Water Works Association and Water Environment Research Foundation have completed a substantial amount of research.


Water distribution systems have many components, including pipes, storage tanks, pumps, and more that deliver water from treatment facilities or water sources to a customer’s tap. Because various parts of distribution systems have the ability to introduce contaminants, like coliform bacteria, lead or copper, to the drinking water, the State Water Board’s Division of Drinking Water oversees how these systems are built, operated, and maintained. Most of the details are spelled out in the California Waterworks Standards.

Emergency interties between neighboring water utilities are common improvements to distribution networks. These inter-connections provide a backup source of water in the event that one city or utility suffers a systematic outage. An added benefit is that interties allow system maintenance without interrupting the flow of water to customers.


Public water suppliers and regulatory agencies face several challenges as they work to implement improvements to drinking water treatment and distribution systems. Older systems need to be replaced, upgraded, and modernized, yet funds for these improvements can be hard to find. Source water protection may help reduce the need for some drinking water treatment, yet can be increasingly difficult to do as the state’s population expands.

The cost of treating and delivering drinking water continues to rise, thanks to higher costs for energy and materials, as well as the higher levels of treatment required. For example, the discovery of new contaminants in drinking water can increase the need for drinking water treatment or for new technologies to be deployed. In general, the cost of pumping, treating, and delivery is captured in the water bills sent to users. Larger systems with more users may have lower per capita water rates than smaller systems with fewer users.

Some financial assistance is available for California public water systems through the Safe Drinking Water State Revolving Fund, Proposition 50, Proposition 84, and the American Recovery and Reinvestment Act of 2009.


The Safe and Affordable Funding for Equity and Resilience (SAFER) program is a comprehensive set of tools, funding sources, and regulatory authorities designed to help struggling water systems sustainably and affordably provide safe drinking water to their customers and meet the goals of safe drinking water for all Californians.   The Fund was established by Senate Bill (SB) 200 in July 2019 to address funding gaps and provide solutions to water systems, especially those serving disadvantaged communities, to address both their short- and long-term drinking water needs.

Click here to download the Drinking Water Treatment and Distribution Resource Management Strategies.



Agencies and organizations working in this area …

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