Despite the importance of potable water to the quality of life, economy, and ecosystems in Los Angeles County, surprisingly little is known about the 228 government and private entities that deliver water, and how vulnerable or resilient they are to withstanding pressures from droughts and climate change. A new study by the UCLA Luskin Center fills this gap and finds that 75% of community drinking water systems in L.A. County exhibit at least one indicator of supply vulnerability due either to dependency on a single type of water source, local groundwater contamination, small size, or a projected increase in extreme heat days over the coming decades.

The Luskin Center’s Los Angeles County Community Water System Atlas and Policy Guide Volume I presents a high-level view of the drinking water systems that serve L.A. County based on in-depth system-level profiles of water sources, service population characteristics, and built environments. This is the most complete, publicly accessible set of maps ever created of L.A. County’s community drinking water systems, which range from major municipal water providers like the L.A. Department of Water and Power, to small utilities serving mobile home parks and remote communities.

The Water Atlas highlights both the County’s vulnerable water systems and the more resilient water systems, based on an investigation of all community water systems that provide drinking water to LA County consumers. Findings of vulnerability include:

• Over a third of the water systems serving L.A. County (79 out of 228 water systems) are 100% dependent on groundwater, an indicator of vulnerability because water systems that rely solely on groundwater may exhaust critical supplies during droughts, are challenged by the presence of local contamination, and have fewer supply alternatives compared to systems with a diversified water supply portfolio. Most of these systems serve small communities in northern LA County, where groundwater withdrawals are not regulated.

• Of every county in the state, L.A. County has the greatest number of community water systems that rely on contaminated groundwater sources: nearly 40% of community water providers in LA County got their water from a groundwater source that exceeded drinking water Maximum Contaminant Levels at least once over the period of 2002-2010.

• L.A. County is home to nearly 100 very small and small community water systems (serving 3,300 or fewer residents year-round) located in both urban and rural areas. These smaller systems often lack the technical, managerial, and financial capacity to withstand the impact of severe drought conditions and overcome water quality and treatment challenges.

• Communities in Azusa, Covina, and El Monte may see over 30 additional days with surface temperatures over 95 °F by 2050, increasing water demand for residential landscapes, public green spaces, and agricultural uses, if these uses are retained.

The state is experiencing its fourth consecutive year of severe drought conditions and new sources of funding are now available for drinking water systems through Proposition 1 and emergency drought relief assistance. Managers of these state funding programs supporting access to safe drinking water and drought resiliency may use this Water Atlas to identify at-risk drinking water systems and disadvantaged populations that have the most to gain from state financial and technical assistance. Policymakers and researchers may use this report to evaluate impacts of state and federal water policies on specific community drinking water systems.

This report is the first in a series of three volumes dedicated to expanding knowledge of drinking water systems in L.A. County, with respect to policies, practices, risks, and opportunities. The approach used in this report is easily scalable and could be applied to every county in the state to inform water policymakers and researchers in California.

The report is available for viewing or download online.