Nearly 4 million people are served drinking water from the Los Angeles Department of Water and Power, making it one of the largest water utilities in the U.S. With the release of the 2025 update of EWG’s Tap Water Database, we took a closer look at this expansive system for the millions of Angelenos served by it, comparing it to the nation as a whole.
In addition to information about L.A. drinking water quality, the Tap Water Database provides details about chemical and radioactive contaminants in the water of nearly 50,000 community systems nationwide.
It also shows how these concentrations compare to federal legal limits and EWG’s own health-based standards for protection against harms such as a greater risk of cancer.
L.A. water is sourced primarily from surface water hundreds of miles away. It is transported to the city via aqueducts, including the State Water Project, the Colorado Aqueduct and the Los Angeles Aqueduct, as well as some local groundwater. From those sources, the water is disinfected at the utility’s treatment plants then piped to the city’s taps.
Test results through 2024 showed 24 contaminants found in the L.A. system, with nine at levels above EWG’s health-based limits.
Key contaminants in Los Angeles tap water
Arsenic
Arsenic is found at over 500 times the EWG health-based limit in L.A.’s drinking water. The contaminant finds its way into taps through natural, industrial and agricultural sources – it leaches from rocks into groundwater that might be used for drinking or irrigation.
Both the Environmental Protection Agency and the World Health Organization have determined that arsenic is a “known human carcinogen,” based on indisputable evidence that arsenic exposures increase the risk of bladder, lung and skin cancer.
Nitrate
The fertilizer chemical nitrate is found in L.A.’s water at levels 12 times EWG’s health guideline. Studies in the U.S. and other countries have found greater incidence of colorectal, ovarian, thyroid, kidney and bladder cancer among people exposed to nitrate in drinking water.
Despite nitrate being associated mostly with rural areas, EWG analyses have found it can be a problem for water systems serving both rural and urban areas. High nitrate levels in large cities’ water systems can be due to upstream pollution from farms, stormwater runoff or the release of municipal wastewater into waterways.
A 2019 peer-reviewed study by EWG found that nitrate pollution in U.S. drinking water may be responsible for up to 12,594 cases of cancer a year, with associated health care costs of up to $1.5 billion.
Uranium
The city’s drinking water contains the radioactive contaminant uranium at levels seven times EWG’s health-based guideline. Uranium causes kidney damage and is known to cause cancer.
Radioactive elements enter groundwater from natural deposits in the earth’s crust. Uranium can be found at higher concentrations in water when human activities such as uranium processing and disposal, mining, or gas and oil drilling or fracking unearth these elements in the rock and soil.
Hexavalent chromium
Hexavalent chromium, or chromium-6, was detected in L.A.’s water at 12 times EWG’s health guideline. A 2008 National Toxicology Program study found water contaminated with chromium-6 causes cancer in laboratory animals, and a 2015 study by researchers in California found an increased risk of stomach cancer in workers exposed to the contaminant.
EWG has long raised the alarm about chromium-6, releasing a landmark analysis and map of the contamination across the U.S. in 2016. EWG maintains the interactive map, which charts contamination utility by utility.
Lead
For the 2025 release of the Tap Water Database, EWG was not able to find lead test results for the L.A. water utility on either state or federal databases. Lead contamination can vary considerably from neighborhood to neighborhood within a city, depending on infrastructure and plumbing materials.
Aging infrastructure is often a key indicator of potential lead contamination in urban areas, since lead pipes were once used in hundreds of cities, most commonly in water lines installed before the 1930s.
Lead is a potent neurotoxin that impairs children’s intellectual development and alters their behavior and ability to concentrate. There is a strong scientific agreement that any amount of lead exposure during childhood is harmful and irreversible.
Disinfection byproducts
The Los Angeles Department of Water and Power page in the Tap Water Database shows that four of the nine contaminants in the system’s water that exceed EWG’s health guidelines are disinfection byproducts, including bromate, the haloacetic acids HAA5 and HAA9, and total trihalomethanes.
Drinking water must be disinfected to kill disease-causing pathogens, and the process is one of the greatest accomplishments in public health. But it can produce toxic byproducts if the water contains organic matter such as soil, fertilizer and animal waste – all of which are likely present in untreated L.A. water.
Scientists have identified more than 600 disinfection byproducts in treated drinking water. Some of the most common are linked to DNA damage, cancer and other harms. In a 2020 study, researchers in Sweden found that pregnant women exposed to low levels of disinfection byproducts in chlorinated drinking water were more likely to give birth to underweight babies.
Water filtration
EWG’s Tap Water Database can help you find the right water filter for your needs. On the utility’s page in the database, you can see what contaminants were found in your system that could be addressed by a particular type of filter.
A simple countertop carbon filter will effectively reduce just four of the nine contaminants in the L.A. system above EWG’s health guideline.
The exceptions are arsenic, chromium-6, nitrate, nitrite and uranium. Results of recent EWG tests of home filters found some pitcher filters can reduce levels of these contamination.
An advanced filter such as reverse osmosis is the most effective way to remove contaminants from drinking water – but this can cost more upfront than a typical carbon filter.
If you’re in the market for a countertop carbon filter, check out EWG’s guide to countertop water filters.
Stay in the know
EWG’s Tap Water Database is a helpful tool even if you’re not an Angeleno. The database puts your tap water’s contamination into perspective, so you can make informed decisions to reduce your exposure.
Once you find your utility in the database, the information provided can help you make informed decisions to help reduce your exposure to contaminants in your drinking water.
In the weeks and months ahead, EWG will continue to produce original drinking water content, from scientific analyses to everyday solutions to eye-opening explainers. Stay in the know by subscribing to EWG’s email list and follow us on Facebook, Instagram and YouTube.
