Fresno County, California: drinking water report. Fresno County sits in the heart of the San Joaquin Valley, with about 1 million residents served by the…
Fresno County sits in the heart of the San Joaquin Valley, with about 1 million residents served by the City of Fresno and dozens of smaller water systems. Fresno draws from both surface water (the Kings River and San Joaquin River systems) and extensive groundwater from the valley's alluvial aquifer. For decades, Fresno was the largest US city relying almost entirely on untreated groundwater – the city did not begin treating its water supply until the Southeast Surface Water Treatment Facility came online in 2004.
The San Joaquin Valley aquifer beneath Fresno has been impacted by decades of agricultural activity. Nitrate contamination is widespread, driven by fertilizer application on surrounding farmland. According to the California State Water Resources Control Board, seven public water systems in Fresno County exceeded the nitrate MCL during the most recent compliance period.
The natural chemistry of the groundwater also presents challenges. The 1,2,3-trichloropropane (TCP) contamination in Fresno's wells – a legacy of pesticide manufacturing – required the city to install granular activated carbon treatment on dozens of wells. UCMR5 data shows PFAS detections in several county systems, adding another layer to an already complex contaminant picture.
Fresno County's water quality varies dramatically between the city system (which has invested in treatment infrastructure) and smaller rural systems that may have limited capacity to address contamination.
Check your water to see data for your specific provider. For nitrate and PFAS, reverse osmosis is the most effective single household treatment. Our water filter guide covers options for the specific contaminant mix found in the San Joaquin Valley. Pull your detailed report, and see our California page for statewide context.