Drinking Water Contaminants

What is drinking water contamination?

Most drinking water in California meets requirements for health and safety. However, the water we drink sometimes becomes contaminated with chemicals or bacteria. Both natural and human sources can contaminate drinking water. Natural sources can be found in rocks and soil or come from fires. Human sources include factories, sewage, and runoff from farms. Poor communities and people in rural areas are exposed to contaminants in their drinking water more often than people in other parts of the state.

Why is this indicator included in CalEnviroScreen?

Numerous chemical and bacterial contaminants are routinely detected in the drinking water in California.
Nitrate from fertilizer or animal manure can leach into groundwater and contaminate wells. Nitrate can cause a blood condition in infants called blue baby syndrome (methemoglobinemia) and may cause birth defects and miscarriages.
Arsenic, a common contaminant, occurs naturally in some rocks and soil and is often found in groundwater in California. Arsenic can cause cancer.

How do we measure drinking water contaminants in CalEnviroScreen 4.0?

The indicator combines information about 14 contaminants and 3 types of water quality violations that are sometimes found when drinking water samples are tested.
We calculated average concentrations for the contaminants in each water system.
To calculate the metric, we matched up the water quality calculation with drinking water system boundaries.
A complete description of the Drinking Water Contaminants indicator can be found in the CalEnviroScreen 4.0 report.

More information on the drinking water indicator:

Methodology for a Statewide Drinking Water Contaminant Indicator (CalEnviroScreen 3.0) See downloads
Drinking Water contaminant results by census tract (Microsoft Excel Spreadsheet) for 4.0: Average concentrations and percentile scores for each contaminant used to calculate the overall drinking water indicator. See downloads
Drinking Water contaminant results by water system or Public Land Survey System (PLSS) section (Microsoft Excel Spreadsheet) for 4.0: Average concentrations for each contaminant in the drinking water indicator by community water system or PLSS section. See downloads
Drinking water service boundaries were extracted from the California Environmental Health Tracking Program's Water Boundary Tool. Currently hosted by the State Water Board's System Area Boundary Layer (SABL) tool.

Where can I find more information on drinking water quality?

Drinking Water Systems with Violations Tool (For more information see the SAFER, Safe and Affordable Fund for Equity and Resilience, Drinking Water Site)
To monitor progress in achieving the human right to water, OEHHA released CalHRTW 1.0 Human Right to Water Report and Tool in January 2021, which assesses the status of water quality, accessibility, and affordability across California.
State Water Resources Control Board: My Water Quality
U.S. Environmental Protection Agency (USEPA): Water on Tap