10 States With The most People Exposed To Contaminated Drinking Water

By Sam Stebbins  •  April 29, 2026
silver faucet with water droplets
Photo by taichi nakamura on Unsplash

The United States is purported to have some of the safest and cleanest drinking water in the world. Across the country, there are approximately 150,000 public water systems that collectively serve about 90% of the U.S. population – and each of these utilities providers are required to meet the safety standards detailed in the Safe Drinking Water Act. But a recent report published by the Environmental Working Group suggests that some of these decades old regulations may be falling short of their stated goal of ensuring access to a contaminant-free tap water. 

Nitrates, often contained in agricultural runoff, can seep into groundwater and pollute public water supplies. At high enough concentrations, these nitrates have been linked to dangerously low blood-oxygen levels in infants. To address this problem, the government imposed a maximum nitrate concentration limit of 10 milligrams per liter in the 1960s for public sources. In the decades since, however, multiple studies have shown that even at concentrations of 2 milligrams per liter, nitrate can pose a grave threat to public health. 

Even at concentrations of 3 milligrams per liter or less, nitrate contamination can increase the risk of certain types of cancer, including thyroid and colorectal. Recent EWG analysis of public water supplies found that approximately 60 million Americans are served by major public systems pumping water at or above this elevated threshold. According to EWG estimates, as many as 12,600 cancer cases may be attributable to elevated nitrate levels.

Using data from EWG’s Tap Water Database, Climate Crisis 247 identified the states where the most people are exposed to potentially harmful levels of nitrate contamination in their drinking water. We reviewed data for all states where at least 1 million people are served by large public water systems with elevated nitrate concentrations – defined as 3 or more milligrams per liter. States are ranked by share of the population exposed to elevated nitrate contaminates using population data from the U.S. Census Bureau’s 2024 American Community Survey. 

Supplemental data on estimated cancer rates linked to nitrate contaminants are as reported by EWG. Agricultural runoff is a leading cause of nitrate contamination in public water supplies, and additional data on farming as a share of state-level GDP is from the Bureau of Economic Analysis. 

10. Ohio

  • Population served by water supply with elevated nitrate contaminates: 18.7% (2,221,966 people)
  • Maximum est. cancer rate attributable to contaminated water: 3.3 cases per 100,000 people
  • Farming industry statewide economic output in 2024: $5.6 billion (0.6% of state GDP)

9. Washington

  • Population served by water supply with elevated nitrate contaminates: 20.0% (1,590,281 people)
  • Maximum est. cancer rate attributable to contaminated water: 3.8 cases per 100,000 people
  • Farming industry statewide economic output in 2024: $5.7 billion (0.7% of state GDP)

8. Utah

  • Population served by water supply with elevated nitrate contaminates: 31.6% (1,106,376 people)
  • Maximum est. cancer rate attributable to contaminated water: 3.3 cases per 100,000 people
  • Farming industry statewide economic output in 2024: $1.2 billion (0.4% of state GDP)
A water tower in the distance with a fountain in the foreground
Photo by Lumin Osity on Unsplash

7. New Jersey

  • Population served by water supply with elevated nitrate contaminates: 33.7% (3,198,762 people)
  • Maximum est. cancer rate attributable to contaminated water: 5.7 cases per 100,000 people
  • Farming industry statewide economic output in 2024: $962.5 million (0.1% of state GDP)

6. Pennsylvania

  • Population served by water supply with elevated nitrate contaminates: 34.9% (4,563,024 people)
  • Maximum est. cancer rate attributable to contaminated water: 9.3 cases per 100,000 people
  • Farming industry statewide economic output in 2024: $3.8 billion (0.4% of state GDP)

5. Nebraska

  • Population served by water supply with elevated nitrate contaminates: 50.5% (1,012,732 people)
  • Maximum est. cancer rate attributable to contaminated water: 7.7 cases per 100,000 people
  • Farming industry statewide economic output in 2024: $9.2 billion (4.9% of state GDP)

4. New Mexico

  • Population served by water supply with elevated nitrate contaminates: 51.9% (1,105,007 people)
  • Maximum est. cancer rate attributable to contaminated water: 3.6 cases per 100,000 people
  • Farming industry statewide economic output in 2024: $1.5 billion (1.0% of state GDP)

3. Nevada

  • Population served by water supply with elevated nitrate contaminates: 53.1% (1,735,933 people)
  • Maximum est. cancer rate attributable to contaminated water: 1.4 cases per 100,000 people
  • Farming industry statewide economic output in 2024: $369.1 million (0.1% of state GDP)

2. California

  • Population served by water supply with elevated nitrate contaminates: 57.6% (22,705,561 people)
  • Maximum est. cancer rate attributable to contaminated water: 10.7 cases per 100,000 people
  • Farming industry statewide economic output in 2024: $35.1 billion (0.9% of state GDP)

1. Arizona

  • Population served by water supply with elevated nitrate contaminates: 68.1% (5,165,863 people)
  • Maximum est. cancer rate attributable to contaminated water: 15.2 cases per 100,000 people
  • Farming industry statewide economic output in 2024: $2.0 billion (0.3% of state GDP)


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