45,812,400 people
Private well water, state by state
All states
| State | Homes on wells | People on wells | Est. above arsenic limit |
|---|---|---|---|
| Vermont | 53.2% | 326,400 | 9,700 |
| Maine | 48.5% | 629,800 | 102,500 |
| New Hampshire | 42.5% | 583,900 | 61,000 |
| Montana | 36.8% | 392,500 | 23,300 |
| Rhode Island | 35.7% | 378,000 | 1,500 |
| Alaska | 33.4% | 205,800 | not modeled |
| Wisconsin | 32.8% | 1,801,800 | 72,700 |
| Michigan | 31.6% | 3,023,300 | 192,700 |
| Wyoming | 28.9% | 161,100 | 6,200 |
| South Dakota | 25.0% | 220,200 | 1,200 |
| Minnesota | 24.5% | 1,279,300 | 80,400 |
| West Virginia | 24.1% | 426,600 | 11,600 |
| Idaho | 23.9% | 423,300 | 47,000 |
| Delaware | 23.5% | 235,500 | 9,900 |
| Virginia | 22.3% | 1,768,200 | 52,800 |
| Iowa | 21.1% | 687,300 | 35,700 |
| Indiana | 20.9% | 1,478,400 | 150,900 |
| Alabama | 20.5% | 1,014,200 | 2,600 |
| Oklahoma | 20.3% | 811,300 | 4,300 |
| Missouri | 20.2% | 1,232,000 | 10,200 |
| South Carolina | 20.1% | 1,038,600 | 28,100 |
| North Dakota | 19.3% | 152,600 | 2,000 |
| Maryland | 19.0% | 1,199,100 | 41,300 |
| Oregon | 19.0% | 815,900 | 26,100 |
| Louisiana | 18.6% | 873,300 | 6,500 |
| Ohio | 18.5% | 2,333,800 | 189,200 |
| Pennsylvania | 18.5% | 2,400,800 | 80,700 |
| Georgia | 18.0% | 1,865,100 | 35,000 |
| Mississippi | 17.3% | 506,500 | 2,800 |
| North Carolina | 17.2% | 1,735,200 | 119,600 |
| Kansas | 16.2% | 496,300 | 6,200 |
| Nebraska | 15.0% | 282,100 | 17,400 |
| Connecticut | 13.1% | 493,400 | 52,100 |
| Tennessee | 13.0% | 859,800 | 5,200 |
| New Mexico | 12.4% | 250,600 | 31,000 |
| New York | 10.3% | 1,784,100 | 66,300 |
| Colorado | 10.2% | 512,400 | 14,300 |
| Washington | 9.8% | 715,300 | 52,200 |
| Illinois | 9.5% | 1,227,200 | 67,700 |
| Massachusetts | 9.1% | 634,900 | 30,500 |
| Florida | 9.0% | 2,017,100 | 50,900 |
| Arizona | 8.9% | 651,400 | 17,000 |
| Texas | 8.2% | 2,241,600 | 95,500 |
| New Jersey | 7.9% | 754,500 | 40,600 |
| Kentucky | 7.1% | 297,100 | 6,700 |
| California | 5.9% | 2,185,200 | 115,800 |
| Hawaii | 4.9% | 64,500 | not modeled |
| Nevada | 4.9% | 142,200 | 21,500 |
| Arkansas | 4.4% | 120,600 | 1,200 |
| Utah | 3.5% | 82,300 | 2,100 |
Well-user counts, arsenic and nitrate figures are each a modeled estimate built from national datasets, not a count of tested wells, and well depths summarize drilling records rather than every well. Your own well can be very different from the county average, which is why the only answer for your home is a lab test. Sources: EPA Office of Research and Development, Water Source 2020 (private well estimates by census block); USGS, county-level domestic well population with arsenic above 10 micrograms per liter (Ayotte and others, 2017) (lower 48 states only).
What to test, and how often
No federal law covers private wells. EPA's drinking water limits apply to public water systems, so testing and treating a private well is up to the owner. EPA and CDC recommend testing at least once a year for coliform bacteria, nitrate, pH and total dissolved solids, and testing for arsenic, uranium, radon and other local concerns based on where you live.
Arsenic is the silent one
USGS estimates about 2,101,600 people in the lower 48 states rely on wells with arsenic above the 10 microgram per liter arsenic limit. It has no taste, color or smell.