Marin County, California: drinking water report. Marin County sits just north of the Golden Gate Bridge with a population of about 260,000.
Marin County sits just north of the Golden Gate Bridge with a population of about 260,000. The Marin Municipal Water District (MMWD) serves most of the county, drawing from seven local reservoirs in the Mount Tamalpais watershed and purchasing supplemental water from Sonoma County's Russian River supply. North Marin Water District serves Novato and surrounding areas. The county's relatively undeveloped watershed produces high-quality source water, but drought vulnerability and aging infrastructure add complexity.
Marin's source water is among the cleanest in the Bay Area, but the distribution system tells a different story in older neighborhoods. According to MMWD's 2024 Lead and Copper Rule monitoring data, lead was detected at the tap in homes with pre-1986 plumbing, with the 90th percentile reading at 8 ppb – below the action level but above the EPA's zero-lead goal.
The EPA's UCMR5 data shows PFAS detections at low levels in the MMWD system. Hamilton Field, a former Army air base in Novato that is now a residential development, has documented PFAS contamination from historical military operations. According to the California DTSC, groundwater remediation at the Hamilton Field site has been ongoing since the 1990s, with PFAS added to the list of contaminants of concern in 2020.
Marin County's water starts clean and generally arrives clean, but older homes with lead plumbing should take precautions. Flushing taps for 30-60 seconds before drinking water after periods of non-use reduces lead exposure from standing water in pipes.
Check your water for data specific to your service area. For lead, a certified pitcher filter is the simplest solution. For PFAS near Hamilton Field, reverse osmosis is more effective. Our water filter guide covers both scenarios. Pull your detailed report for trend data, and visit our California page for statewide context.