Mapping America's Worst Drinking-Water Violations

Nearly three in ten community water systems in the United States have a health-based Safe Drinking Water Act violation on their record since 2016. But where that risk concentrates depends entirely on how you count it — and two states sit at opposite ends of the two ways of measuring.

An AGUACYCLE analysis of EPA's Safe Drinking Water Information System, covering violations recorded since 2016 through the first quarter of 2026, shows 14,233 of the nation's 48,769 active community water systems — 29 percent — with at least one health-based violation. Of those, 11,592 remain unresolved.

Rates versus raw counts

By raw count, Texas leads the country with 1,723 systems in violation, followed by California with 1,014, Pennsylvania with 724, Oklahoma with 653, Louisiana with 517, and North Carolina with 471. Those are mostly the big, populous states — they have more water systems, so they accumulate more violations.

Adjust for the size of each state's system inventory and a very different map appears. Among states with at least 50 community water systems, Oklahoma posts the highest violation rate in the nation: 73.9 percent of its systems carry a health-based violation. New Mexico follows at 68.8 percent, Louisiana at 63.1 percent, West Virginia at 60.5 percent, Alaska at 59.8 percent, and Kentucky at 47.7 percent.

The contrast is sharpest in Oklahoma itself. The state is fifth by raw count but first by rate — meaning the problem is not a handful of troubled utilities but something close to the norm across its water systems.

What drives the clustering

The states topping the rate list share a profile: large numbers of very small, rural water systems serving few customers each. A system serving a few hundred people has the same federal testing and treatment obligations as a big-city utility but a fraction of the revenue, engineering staff, and ratepayer base to meet them. That structural disadvantage shows up as chronic violations.

Agriculture compounds it. Several of the highest-rate states sit in heavily farmed regions where nitrate from fertilizer and animal operations seeps into the shallow groundwater that small systems depend on, pushing them past federal limits and forcing treatment many cannot afford.

The affordability trap

Fixing a small system's violation often means new treatment equipment or consolidation with a neighbor — capital that rural systems rarely have on hand. The result is a self-reinforcing loop in which the communities least able to pay for clean water are the ones most likely to be drinking water that breaks federal standards. That is why raw counts can be politically convenient but analytically misleading: a low-population state can have a small absolute number of violations and still expose a large share of its residents to substandard water.

The EPA data is public and updated continuously, but it captures only what systems report and what regulators record. The true national picture is likely worse at the margins, where the smallest systems test least often.