Nitrate in Well Water
Nitrate enters groundwater from fertilizer, animal waste and septic systems, making it one of the most widespread private-well contaminants — especially in agricultural areas. Like arsenic, it's invisible and tasteless.
Why it's dangerous
High nitrate is most dangerous for infants under six months: it interferes with the blood's ability to carry oxygen, causing "blue baby syndrome" (methemoglobinemia). Pregnant women and adults face risks at sustained high levels too. Never mix infant formula with well water that hasn't been tested for nitrate.
The EPA limit
The federal MCL for nitrate (measured as nitrogen) is 10 mg/L. Boiling water does not help — it concentrates nitrate, making it worse.
States with the highest modeled risk
Share of private-well residents above the 10 mg/L limit (USGS model):
- Delaware 12.7%
- California 10.4%
- Maryland 6%
- Oklahoma 6%
- Kansas 5.2%
- Pennsylvania 3.9%
- Idaho 3.7%
- Texas 2.5%
Nitrate in well water near you: check your state
Nitrate is local — it follows fields, feedlots and septic density — so your county matters more than your state. Pick your state for its county-by-county breakdown. The first figures are the USGS-modeled private-well residents above 10 mg/L; the last column is the county where the most USGS-sampled wells actually tested over the limit.
| State | Well residents over 10 mg/L | Highest measured county |
|---|---|---|
| Delaware | ~17,900 (12.7%) | Sussex County 24% of 164 wells |
| California | ~144,000 (10.4%) | Fresno County 36% of 229 wells |
| Maryland | ~43,300 (6%) | Kent County 24% of 92 wells |
| Oklahoma | ~28,300 (6%) | Caddo County 29% of 7 wells |
| Kansas | ~12,600 (5.2%) | Brown County 50% of 6 wells |
| Pennsylvania | ~85,900 (3.9%) | Blair County 56% of 9 wells |
| Idaho | ~11,800 (3.7%) | Washington County 27% of 44 wells |
| Texas | ~40,800 (2.5%) | Terry County 60% of 20 wells |
| Washington | ~14,700 (2.2%) | Franklin County 34% of 77 wells |
| Nebraska | ~5,060 (2.2%) | Hitchcock County 67% of 6 wells |
| New Mexico | ~3,530 (1.3%) | Sierra County 8% of 12 wells |
| Arizona | ~3,060 (1.3%) | Maricopa County 26% of 207 wells |
| Wyoming | ~1,430 (1.3%) | Park County 10% of 20 wells |
| New Jersey | ~8,500 (1.1%) | Salem County 43% of 68 wells |
| Wisconsin | ~12,500 (0.8%) | Winnebago County 40% of 5 wells |
| Colorado | ~2,500 (0.7%) | Weld County 50% of 66 wells |
| West Virginia | ~2,520 (0.6%) | Jefferson County 23% of 93 wells |
| Iowa | ~2,160 (0.4%) | Butler County 33% of 6 wells |
| Kentucky | ~801 (0.2%) | — |
| Utah | ~168 (0.2%) | Box Elder County 10% of 48 wells |
| Tennessee | ~794 (0.1%) | Greene County 40% of 5 wells |
| Indiana | ~711 (0.1%) | Wayne County 31% of 13 wells |
| Oregon | ~697 (0.1%) | Marion County 27% of 11 wells |
| South Carolina | ~563 (0.1%) | Allendale County 60% of 5 wells |
| Montana | ~246 (0.1%) | Valley County 45% of 40 wells |
| South Dakota | ~146 (0.1%) | Meade County 12% of 17 wells |
| Florida | ~548 (<0.1%) | Polk County 34% of 94 wells |
| Michigan | ~530 (<0.1%) | Hillsdale County 14% of 7 wells |
| Minnesota | ~441 (<0.1%) | Sherburne County 46% of 48 wells |
| North Carolina | ~370 (<0.1%) | Sampson County 59% of 29 wells |
| Georgia | ~304 (<0.1%) | Worth County 23% of 13 wells |
| Illinois | ~296 (<0.1%) | Kankakee County 44% of 9 wells |
| Virginia | ~46 (<0.1%) | Suffolk 11% of 9 wells |
| Alabama | ~35 (<0.1%) | Tuscaloosa County 17% of 6 wells |
| Missouri | ~32 (<0.1%) | Barton County 20% of 5 wells |
| Rhode Island | ~11 (<0.1%) | Washington County 4% of 80 wells |
| Arkansas | ~4 (<0.1%) | Van Buren County 8% of 25 wells |
| Nevada | none modeled | Washoe County 14% of 165 wells |
| North Dakota | none modeled | Grand Forks County 17% of 6 wells |
| Vermont | none modeled | Orange County 14% of 7 wells |
| Louisiana | none modeled | Red River County 7% of 15 wells |
| Mississippi | none modeled | Bolivar County 11% of 9 wells |
| Connecticut | none modeled | New London County 21% of 28 wells |
| District of Columbia | none modeled | — |
| Massachusetts | none modeled | Hampden County 15% of 13 wells |
| New York | none modeled | Kings County 15% of 27 wells |
| Ohio | none modeled | Champaign County 16% of 19 wells |
| Maine | none modeled | Cumberland County 5% of 22 wells |
| New Hampshire | none modeled | — |
Modeled and sampled-well figures describe an area, not your tap — a lab test is the only way to know your own well's nitrate level.
How to remove nitrate
Carbon filters and standard softeners do not remove nitrate. Use reverse osmosis (NSF/ANSI 58) or a nitrate-specific anion-exchange system. Reverse osmosis is the simplest point-of-use fix for drinking and cooking water.
Match the filter to your test result
Carbon pitchers and faucet filters do not remove arsenic or nitrate. Reverse osmosis is the point-of-use fix; a whole-house system handles the rest of the home.
APEC ROES-50 5-Stage Reverse Osmosis System
5-stage RO, ★ 4.7 — removes arsenic, nitrate, lead, fluoride and PFAS.
Check price on Amazon →Whole-house well water system
Treats every tap, shower and appliance — the right scale for sediment, iron, sulfur and bacteria on a private well.
Compare on Amazon →Waterdrop reverse-osmosis systems
Under-sink RO removes arsenic, nitrate, lead and PFAS at the kitchen tap.
Shop on Waterdrop direct →Affiliate links — we may earn a commission at no extra cost to you. Re-test after installing to confirm the system is working.