Johnston, IA vs Des Moines, IA

When comparing tap water quality between Johnston, IA and Des Moines, IA, Johnston currently holds a noticeable 7-point lead in average WaterQ score, with a score of 83 out of 100 versus 76 for Des Moines. 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.

Des Moines, IA is the larger of the two, with 228,387 more residents than Johnston, yet both cities are served by the same number of public water systems (2). 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 Johnston or Des Moines, 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 Johnston or Des Moines 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.