San Juan County Water Quality

San Juan County, Washington has a drinking-water quality grade of F with a score of 4.1/100, based on EPA SDWIS compliance data. The county has 145 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and live streamflow are reported separately on this page.

San Juan County has 145 health-based drinking water violations recorded by the EPA over the past 5 years. Health-based violations indicate instances where contaminant levels exceeded EPA Maximum Contaminant Levels (MCLs). Violations may have been resolved — check with your local water utility for current status.

EPA's Water Quality Portal records 45,662 measurements from 9 monitoring sites in San Juan County over the past five years. The most frequently measured characteristic groups are Physical, Not Assigned, Nutrient. Each measurement is a single sample analyzed for one characteristic (E. coli, pH, dissolved oxygen, etc.). High monitoring density means more scientific evidence behind any reported signal — it does not by itself indicate water quality.

San Juan County's SDWIS water quality score of 4.1/100 is lower than the Washington state average of 59.3. The average water quality grade across Washington is D, based on data from 39 counties with available SDWIS data.

Based on EPA SDWIS data, San Juan County has a water quality grade of F (4.1/100). This indicates below-average compliance with significant violations. Residents may want to consider home water filtration or independent testing. The grade speaks to the public water system, not the watershed — for watershed-level concerns, see the Watershed Health zone. For the most up-to-date information, contact your local water utility or review your Consumer Confidence Report (CCR).

San Juan County has 145 health-based drinking water violations on record from the EPA SDWIS database. A higher violation count can result from aging infrastructure, underfunded water utilities, agricultural runoff contamination, or industrial pollution. Counties with more water systems may also see more violations simply due to scale. Residents concerned about water quality should consider independent water testing and home filtration systems.

San Juan County ranks #37 out of 39 counties in Washington by SDWIS water quality score (1 = best). With a score of 4.1/100, it falls in the bottom third of counties statewide. The ranking reflects EPA SDWIS compliance only — not watershed impairment, monitoring density, or streamflow, which are tracked separately on this page.