O Fallon, MO vs St. Louis, MO

When comparing tap water quality between O Fallon, MO and St. Louis, MO, O Fallon currently holds a substantial 23-point lead in average WaterQ score, with a score of 82 out of 100 versus 59 for St. Louis. O Fallon, MO carries a B grade while St. Louis, MO carries a D. 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.

St. Louis, MO is the larger of the two, with 177,752 more residents than O Fallon. O Fallon is served by 5 public water systems, compared with 3 in St. Louis — a difference of 2 systems. A larger number of systems often reflects a more fragmented distribution network spanning multiple utilities, suburbs, or rural service areas, while a single large utility serving a big population can benefit from economies of scale in treatment and monitoring, but may also face more complex, aging infrastructure to maintain.

For residents of either O Fallon or St. Louis, 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 O Fallon or St. Louis 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.