Best and Worst Counties for Water Quality in America

Water quality is not evenly distributed across America. Some counties have pristine, fully compliant water systems with zero health violations on record. Others face persistent compliance challenges that put them at the bottom of national rankings. We ranked all US counties by water quality score — a percentile-based measure of EPA compliance — to find the 25 best and 25 worst counties for drinking water.

The gap is substantial. The best counties score 95 or above, indicating near-perfect compliance records. The worst score below 10, reflecting repeated health-based violations across their water systems. Geographic and economic patterns are unmistakable.

The 25 Best Counties for Water Quality in America

These counties have the highest water quality scores in the nation. Most have zero or near-zero health-based violations and strong overall compliance records:

Geographic Patterns: Where the Best Water Is

The best counties for water quality cluster in specific regions. Alabama (25 counties) dominate the top 25. Several factors explain why:

• Protected water sources: Many top counties rely on deep groundwater aquifers or protected surface water reservoirs with limited agricultural or industrial contamination.
• Newer infrastructure: Counties that built or upgraded water systems more recently face fewer compliance issues related to aging pipes and outdated treatment.
• Lower agricultural intensity: Less fertilizer and pesticide use means less contamination of source water, particularly from nitrates.
• Strong state oversight: Some states enforce drinking water standards more rigorously than others, resulting in better compliance across their counties.

The 25 Worst Counties for Water Quality in America

These counties have the lowest water quality scores, reflecting persistent compliance challenges:

What the Worst-Ranked Counties Have in Common

The counties at the bottom of the rankings share several characteristics. Texas (10 counties), Oklahoma (6 counties), Alaska (3 counties), Georgia (2 counties), Montana (1 counties) are most represented among the worst 25. Common factors include:

• Aging water infrastructure: Many of these counties have water systems built decades ago that have not been sufficiently upgraded. Lead service lines, corroding pipes, and outdated treatment facilities contribute to violations.
• Small, underfunded systems: Rural counties often have multiple small water systems, each serving a few hundred people. These systems lack the revenue base to hire full-time water treatment operators or invest in modern equipment.
• Agricultural and industrial contamination: Counties in farming regions face nitrate contamination from fertilizer runoff. Former industrial areas may have legacy contamination that affects source water.
• Inconsistent monitoring: Some of the worst-ranked counties have monitoring violations in addition to health-based violations, suggesting systemic capacity issues rather than one-time events.

The Rural-Urban Divide in Water Quality

One of the clearest patterns in the data is the rural-urban divide. Large urban water systems — serving hundreds of thousands of people — tend to have professional staff, dedicated budgets, and modern treatment facilities. They score well.

Small rural systems face different challenges. A system serving 200 people cannot justify the same infrastructure investments as one serving 200,000. Many rural systems rely on a single part-time operator. When that operator retires or leaves, compliance can suffer.

This does not mean rural water is inherently unsafe. Many rural counties score in the top 25. But the worst-ranked counties are disproportionately rural, reflecting a funding and capacity gap rather than a fundamental water quality difference.

Methodology

Water quality scores use percentile-rank methodology based on EPA SDWIS violation data. Each county is ranked against all US counties with available data. Health-based violations (MCL and treatment technique violations) carry the most weight. Scores range from 0 (worst) to 100 (best). Letter grades: A (90-100), B (75-89), C (60-74), D (40-59), F (0-39). Data sourced from EPA ECHO API. See our methodology page for full details.