Madera County, California: drinking water report. Madera County straddles the San Joaquin Valley and the Sierra Nevada foothills, with about 157,000…
Madera County straddles the San Joaquin Valley and the Sierra Nevada foothills, with about 157,000 residents. The city of Madera and surrounding communities draw from groundwater and, to a lesser extent, surface diversions from the San Joaquin River. Agriculture is the economic backbone – wine grapes, almonds, pistachios, and dairy operations cover the valley floor. The county's water story is one of diminishing supply and deteriorating quality as the aquifer declines.
Nitrate contamination mirrors the pattern across the Central Valley. According to the California State Water Board's 2024 compliance data, 14 community water systems in Madera County have reported nitrate levels above 50% of the MCL. Small, unincorporated communities along the Highway 99 corridor are most affected, often lacking the financial resources to install treatment.
The pesticide DBCP (dibromochloropropane), banned in 1977 but persistent in groundwater, continues to show up in Madera County wells. A 2024 State Water Board investigation found DBCP at detectable levels in 6 production wells in the county. The compound's association with male reproductive harm makes it a concern even at low concentrations.
The Central Valley groundwater crisis affects Madera County acutely. Wells are going deeper, water quality is shifting, and small communities bear a disproportionate burden. If your water system has issued any violation notices, take them seriously.
Check your water for the latest data on your supply. For the mix of nitrate, legacy pesticides, and naturally occurring contaminants, reverse osmosis provides the most comprehensive household protection. Our water filter guide covers Central Valley-specific scenarios. Pull your detailed report for historical context, and visit our California page for statewide data.
Drinking water is one exposure route. These federal datasets also cover Madera County, CA.
The EPA places Madera County, CA in Zone 2 - a moderate-risk category, with a predicted average indoor radon level between 2 and 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
40% of homes in Madera County, CA were built before 1980, and 8% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Madera County, CA averages 9.1 µg/m³, above the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
Across 55 public water systems serving Madera County, CA with EPA lead testing on record, 3 (5.5%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 5 ppb. 29 water systems serving Madera County, CA carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Arsenic | 15 |
| Lead and Copper Rule Revisions | 10 |
| Combined Uranium | 7 |
| Gross Alpha Particle Activity | 6 |
| Total Coliform Rule | 4 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.