This feature set provides locations where water testing exceed the Maximum Contaminant Levels (MCLs) established by the California State Water Resources Control Board. The water tests were collected by the San Francisco Estuary Partnership alongside community-based partners and Tribes from around the San Francisco Bay Region. While the tap water testing project was conducted to provide useful insight into water quality in the region, participants were self-selected. The effort was designed to test the water of those who expressed concern and had a desire to learn more to understand potential issues and their solutions and this effort should not be construed to be a rigorous scientific study.

Drinking water standards are called maximum contaminant levels. MCLs are found in Title 22 of the California Code of Regulations.

MCLs are adopted as regulations. They are health protective drinking water standards to be met by public water systems. MCLs take into account not only chemicals' health risks but also factors such as their detectability and treatability, as well as costs of treatment. Health & Safety Code §116365(a) requires a contaminant's MCL to be established at a level as close to its PHG as is technologically and economically feasible, placing primary emphasis on the protection of public health.

Additional information on MCLs is provided by the California State Water Resources Control Board's Contaminants in Drinking Water page.

This data set was collected through a California Department of Water Resources grant that worked with disadvantaged and underserved communities and Tribes to collect data on tap water quality throughout the region in response to distrust in tap water documented during the San Francisco Bay Regional Water Needs Assessment. This tap water testing effort was envisioned and implemented by the community and Tribal partners that the San Francisco Estuary Partnership worked with during the Regional Water Needs Assessment Process and was supported technically and programmatically by the San Francisco Estuary Partnership, UCLA Luskin Center, Woodard and Curran, and Lotus Water. All of the locations have been slightly modified (between 0.5 and 2.5 blocks) to protect the personal information of the project participants.