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About 1 million California residents live in areas served by water systems that are failing to supply clean drinking water. More than 300 of the state’s water systems have levels of contamination higher than what the state allows. In dozens of places, tainted water is making its way from the source to the tap, potentially causing serious health consequences for those who drink it.

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California has two thresholds to assess water quality. The public health goal allows for small amounts of contaminants that do not pose a significant health risk. The maximum contaminant level is a legal threshold that is sometimes higher than the public health goal. The MCL is set as close as possible to the public health goal, while also accommodating the technological limitations of detecting contaminants in the water and treatment costs.

Water systems are required to test their sources on a regular basis and report the results to the California State Water Resources Control Board. Violations are issued when contamination exceeds the MCL and is not resolved through water treatment or by purchasing clean water from another system. Additionally, if a water system is unable to address contamination issues, it must notify customers on how to use the water safely.

The Times has compiled violation records, monitoring results and contamination notices for the three most common contaminants – arsenic, nitrate and 1,2,3-Trichloropropane (1,2,3-TCP) – from all 3,200 public water systems in California. Look up your water supplier using the drop-down menus below.

Find a water provider

The most reliable way to find your provider is to check your water bill. If you don't have a water bill, you can look up providers near you.

These providers recently sent notices of contaminated water

Within the last three years, 81 providers served water that had levels above the maximum contaminant level for arsenic, nitrates or 1,2,3-TCP.




Los Angeles




San Benito

San Bernardino

San Diego

San Joaquin

Santa Clara



What does failing mean?

If your water system is failing, that means it’s not meeting one or more goals of the Human Right to Water Act, which states that all Californians have a right to safe, affordable and accessible water for drinking, cooking and sanitation, and that providers are maintaining a sustainable water system. These systems are out of compliance or regularly violate primary drinking water standards. A system that is failing doesn’t necessarily mean it is serving contaminated water.

The water provider lookup above includes failing designations as of September 2023. For more information about the risks your public water system is facing, including up-to-date failing status, how they’re assessed and more, visit the State Water Board’s SAFER Dashboard. Here’s a user guide to help you navigate the site.

What is the maximum contaminant level?

The maximum contaminant level is the highest allowable amount of a contaminant in water. The Environmental Protection Agency establishes MCLs, but states can adopt more stringent standards or develop them for contaminants that the federal government hasn’t covered.

If your provider is exceeding a primary MCL, you should have received a drinking water contamination notice, which may contain information about what your provider is doing to remediate the problem and when it may be resolved.

The top three contaminants in drinking water in California are arsenic, nitrate, and 1,2,3,-trichloropropane (1,2,3 - TCP), affecting 228 of the failing systems.

Arsenic10 parts per billion
Nitrate10 parts per million
1,2,3-TCP5 parts per trillion

What is the public health goal?

Public health goals are set by California's Office of Environmental Health Hazard Assessment to the level below which a drinking water contaminant does not pose a significant health risk. For some contaminants, arsenic and 1,2,3-TCP included, the goal is much lower than the MCL. This is due to technological and cost limitations in testing for these chemicals at the lower level at scale. Many labs across the state are not equipped to detect these chemicals at the lower public health goal level.

Arsenic0.004 parts per billion
Nitrate10 parts per million
1,2,3-TCP0.07 parts per trillion

What are the risks of drinking water with arsenic, nitrate or 1,2,3-TCP?

Arsenic: Long-term exposure to high levels of arsenic from drinking water has been linked to cancer of the bladder, skin and lungs. It can also cause nausea, vomiting, diarrhea, muscle cramping, numbness in the fingers and toes, partial paralysis and skin abnormalities such as discoloration or lesions. It’s been associated with harmful effects on children’s cognitive development and decreased mental abilities among adults.

The World Health Organization says that water with low levels of arsenic can be used for drinking and cooking.

Bathing and washing clothes with arsenic-tainted water are generally considered safe. Brushing your teeth, washing dishes and food, and watering your garden are OK too, according to the State Water Board.

Nitrate: Ingesting water with high nitrate concentrations has been linked to methemoglobinemia, a potentially life-threatening disorder that makes it harder for red blood cells to carry oxygen through the body. Symptoms may include blue or purple skin, nails and lips.

Infants may develop shortness of breath and develop “blue baby syndrome.” Pregnant people are also more vulnerable to illness.

Recently, drinking water with high levels of nitrate has also been linked to thyroid cancer.

Nitrate is not absorbed through the skin, so it is OK to bathe or shower babies and children in water contaminated with nitrate, according to the California Department of Public Health. Brushing your teeth, washing dishes and food, and watering your garden are OK too, according to the State Water Board.

1,2,3-TCP: Exposure to 1,2,3-TCP can occur through skin contact, ingesting or cooking with contaminated water, or by inhaling vapors while showering, bathing or washing dishes.

Short-term exposure can cause eye, throat and skin irritation, and may affect memory, concentration and muscle coordination. Animal studies show that long-term exposure can cause cancer, lead to lower body weight, and damage liver, nose, kidneys and lungs.

For more information about these contaminants and others, visit the Agency for Toxic Substances and Disease Registry’s website.

It’s important to note that boiling water may kill bacteria and other pathogens, but it can concentrate contaminants such as arsenic and nitrate.

What can I do if my water is unsafe to drink?

State funding may be available to provide urgent drinking water, such as bottled or hauled water, to water systems serving small and disadvantaged communities with contaminated taps.

Your water system must apply to the State Water Board. Visit the board’s CAA Urgent Drinking Water Need Projects webpage for the application and more information.

Domestic wells and “state small water systems” – which serve at least five and up to 14 connections, and provide drinking water to fewer than 25 people – are regulated by counties, not the state, so they are not required to test for the same contaminants as public water systems. If you’re concerned about contamination, there are laboratories that will test your water. To find a certified lab near you, visit the State Water Board’s Geographic Information System Map.

If you’re a domestic well owner or in a state small water system with drought-related or water contamination issues in a disadvantaged or low-income community, there may be state funding available to help you.

Organizations such as Self-Help Enterprises, Valley Water Collaborative and the Community Water Center, as well as Shasta and Santa Cruz counties, operate regional programs through the State Water Board that offer a range of services related to drinking water, such as water testing, bottled water, and/or water treatment if contaminants are found. Visit the board’s website to learn about where they operate and the programs and services they can provide.

Counties or eligible partners can apply for funding to help residents served by domestic wells or state small water systems, and they will be responsible for managing and implementing the program. Visit the State Water Board’s County-wide and Regional Funding Programs for more information.

More information about what to do if your water is unsafe to drink can be found in English and Spanish on the Community Water Center’s website.