Answer: It's a big difference, not a small one.
Community water systems in the poorest quarter of U.S. counties (avg. poverty rate 19.7%, avg. median household income $55,121) had 36.7% of systems record at least one health-based Safe Drinking Water Act violation between 2015-2024, versus 23.7% in the least-poor quarter of counties (avg. poverty 7.7%, avg. median income $98,121) — a 1.55x gap in violation incidence.
Weighted by population served, the gap is far starker: 114.0 health-based violations per 100,000 people served in the poorest quartile vs. 24.7 per 100,000 in the least-poor quartile — a 4.6x disparity. Both total and health-based violations per system rise steadily and monotonically with county poverty across all four quartiles (avg. violations/system: 19 → 20 → 25 → 35; avg. health-based violations/system: 1 → 1 → 2 → 5).
Joined EPA SDWIS active Community Water Systems (environment.drinking_water, pws_type_code='CWS')
to their county via the HUD/USPS ZIP-to-county crosswalk (best-match county by address ratio), then
to Census SAIPE county poverty rate and median household income for 2023 (the crosswalk's and
SAIPE's most recent overlapping vintage — 2022 has no SAIPE county estimate; SAIPE jumps 2020→2023).
Counted SDWA violations 2015-2024 per system from environment.drinking_water_violations, split
into all violations and health-based violations (is_health_based='Y'). Systems were split into
county-poverty quartiles (engine quantile_cont breakpoints: 9.3%, 12.0%, 15.2%) and aggregated:
share of systems with any health violation, average violations per system, and health violations
per 100,000 population served. n = 39,518 systems.
| Poverty quartile | Avg poverty rate | Avg median income | n systems | Pop served | % systems w/ health violation | Avg total viol./system | Avg health viol./system | Health viol. / 100k served |
|---|---|---|---|---|---|---|---|---|
| Q1 (lowest) | 7.7% | $98,121 | 9,980 | 61.8M | 23.72% | 19 | 1 | 24.74 |
| Q2 | 10.7% | $77,224 | 9,937 | 63.1M | 26.46% | 20 | 1 | 29.43 |
| Q3 | 13.6% | $69,398 | 9,961 | 75.3M | 26.41% | 25 | 2 | 29.66 |
| Q4 (highest) | 19.7% | $55,121 | 9,640 | 50.0M | 36.66% | 35 | 5 | 113.995 |
This matches, and sharpens, the environmental-justice literature: - Allaire et al. 2022 (AWWA Water Science) find low-income communities ~1.77 percentage points more likely to have a health-based violation nationally. - Schaider et al. 2018 (Environmental Health) find socioeconomic disparities specifically in nitrate contamination. - PLOS Water 2024 finds disparities across nearly every water-quality indicator, concentrated in small, underfunded systems serving low-income and rural areas; American Indian-served systems face 2-3x more health-based violations.
The 1.55x incidence gap and especially the 4.6x per-capita gap computed here are larger than a simple percentage-point comparison because per-capita weighting is far more sensitive to a relatively small number of very poor, small/rural systems that rack up many repeated health-based violations — exactly the mechanism (underfunded small systems concentrated in poor areas) the literature identifies as the driver.
drinking_water_violations / drinking_water (AskAmerica environment schema, Envirofacts, snapshot through 2026-03)saipe_poverty (AskAmerica census schema, county level, 2023 vintage)geo.zip_county_crosswalk, 2023 vintage)dashboard.png — full published report dashboard (stat tiles + both bar charts)chart_health_violation_pct.png — standalone bar chart of % systems with health-based violation by poverty quartile