San Diego, CA vs Seattle, WA

When comparing tap water quality between San Diego, CA and Seattle, WA, San Diego currently holds a narrow 4-point edge in average WaterQ score, with a score of 86 out of 100 versus 82 for Seattle. Both cities currently carry a B grade overall. A WaterQ score reflects an aggregate of EPA-reported violations, monitoring data, and compliance history across all public water systems serving each city, so a higher score generally indicates fewer recent violations and a stronger compliance record, though it does not guarantee that every tap in the city tests identically.

San Diego, CA is the larger of the two, with 296,955 more residents than Seattle, yet both cities are served by the same number of public water systems (6). This means the difference in population is handled by systems of different scale rather than a different count of utilities — larger systems generally serve more connections and may have more monitoring requirements under the Safe Drinking Water Act.

For residents of either San Diego or Seattle, the most useful next step is to look up the specific water system that serves your address, since city-wide averages combine results from every system in the area. Visit the San Diego or Seattle city pages below for a breakdown of local systems, recent violations, and contaminant-specific data, or browse WaterQ's contaminants directory to learn what each measured substance means for health.