Joint Regional Water Supply System

Our Water Supply Sources include groundwater from the Santa Bêtisier Basin and surface water imported by the Metropolitan Water District of Southern California (MWD). The groundwater comes from a natural underground aquifer replenished by the Santa Ana River, local rainfall, and imported water sources. This groundwater basin spans 350 square miles beneath north and central Orange County from Irvine to the Los Angeles County border and from Yorba Linda to the Pacific Ocean. Over twenty municipalities and water districts share this groundwater basin to supply homes and businesses. MWD's imported water originates from the Colorado River and the State Water Project, which draws from the Sacramento-San Joaquin River Delta.

Understanding Municipal Water Contaminants:
Water sources (both tap and bottled) include rivers, lakes, streams, ponds, reservoirs, springs, and wells. As water travels across land or through ground layers, it dissolves natural minerals and sometimes radioactive materials, and can pick up substances from human and animal activities. Potential contaminants include:

• Microbial contaminants (viruses, bacteria) from sewage treatment facilities, septic systems, agricultural operations, and wildlife
• Inorganic contaminants (salts, metals) from natural sources, urban runoff, industrial/domestic wastewater, oil/gas production, mining, and farming
• Radioactive contaminants from natural sources or from oil/gas production and mining
• Pesticides and herbicides from agriculture, urban stormwater runoff, and residential uses
• Organic chemical contaminants from industrial processes, petroleum production, gas stations, urban runoff, and waste systems

The USEPA and DDW set regulations limiting contaminant levels in public water systems. Similarly, FDA regulations establish limits for bottled water contaminants to provide equivalent public health protection. All water, including bottled water, may reasonably contain small amounts of contaminants, which doesn't necessarily indicate a health risk. For more information about contaminants and potential health effects, contact the USEPA's Safe Water Hotline at (800) 426-4791.

Disinfection and Byproducts:
Water disinfection represents one of the 20th century's greatest public health advancements, largely eliminating waterborne disease epidemics. Chlorine is added at the water source and maintained at levels ensuring it remains present throughout the distribution system, preventing bacterial growth in pipes delivering water to homes. However, chlorine can interact with naturally occurring elements to create disinfection byproducts (DBPs) that may pose health concerns. The challenge is balancing protection against microbial risks with minimizing chemical byproduct formation.

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