The Environmental Working Group released a first-of-its-kind interactive map in April 2026 showing more than 6,000 community water systems — serving more than 62.1 million Americans — provide tap water with nitrate concentrations at or above 3 milligrams per liter (mg/L). The map is searchable by zip code and is built from 2021–2023 utility monitoring data covering all 50 states. EWG’s analysis is the most granular national look at nitrate contamination in U.S. drinking water to date, and it documents that risk extends far below the EPA’s enforceable limit of 10 mg/L.
What the Data Shows
EWG used utility-reported nitrate measurements from 2021 to 2023 to build a tiered exposure map. The thresholds matter because peer-reviewed epidemiology has documented health effects at concentrations well below the federal Maximum Contaminant Level (MCL) of 10 mg/L:
| Nitrate Level | Systems | People Served | Health Concerns |
|---|---|---|---|
| ≥ 3 mg/L | 6,000+ | 62.1 million | Thyroid disease; gastric, kidney, bladder, colon cancer; preterm birth; birth defects |
| ≥ 5 mg/L | 3,200+ | (subset of above) | Adds documented colorectal and ovarian cancer risk |
| ≥ 10 mg/L (federal MCL) | 606 | 3+ million | Methemoglobinemia (“blue baby syndrome”); regulatory violation |
The 10 mg/L EPA standard was set in 1962 to prevent acute methemoglobinemia in infants. It has not been revised in more than six decades, even as research has accumulated linking far lower exposures to long-term cancer risk. EWG’s mapping makes the gap between “legal” and “safe” visible at the household level for the first time.
How Nitrate Gets Into Drinking Water
Nitrate in U.S. drinking water comes overwhelmingly from agriculture. Synthetic nitrogen fertilizers applied to corn, soybeans, and other row crops, along with manure runoff from concentrated animal feeding operations (CAFOs), wash into surface water and leach into shallow groundwater. From there, nitrate reaches public water intakes and private wells — often miles downstream of the application site.
The pattern is geographically concentrated. The Corn Belt — Iowa, Illinois, Indiana, Nebraska, Minnesota, parts of Kansas, the Dakotas, and Wisconsin — sees the heaviest exposure. Central California’s Central Valley, eastern North Carolina’s hog-farming corridor, and the Texas Panhandle also rank high. Rural communities and private well users typically face higher concentrations than residents of large metro systems, partly because shallow rural aquifers respond faster to surface application and partly because small water systems often lack the treatment infrastructure to remove nitrate.
For a deeper look at how nitrate moves from field to tap and the specific health pathways involved, see the nitrate contaminant profile.
Why the 10 mg/L Standard Misses the Risk
The EPA’s nitrate MCL was based on a single endpoint: preventing severe methemoglobinemia, a blood disorder that prevents oxygen delivery and can be fatal in infants under six months. That risk is real — and the 10 mg/L standard does largely prevent it — but the standard does not account for chronic exposure outcomes that have since been documented in large epidemiological studies:
- Colorectal cancer at long-term exposure as low as 5 mg/L (Iowa Women’s Health Study, 2018)
- Ovarian and bladder cancers at similar exposures
- Thyroid disease, including hypothyroidism, at chronic exposure levels in the 3–5 mg/L range
- Preterm birth and birth defects in pregnancies exposed to elevated nitrate in drinking water
- Methemoglobinemia in adults with specific genetic susceptibilities, even below 10 mg/L
EWG and a number of public health researchers have proposed a health-based guideline closer to 0.14 mg/L for cancer prevention — roughly 70 times stricter than the federal MCL. That figure is not a regulatory standard; it’s a risk-based number derived from cancer dose-response data.
What This Means for Pregnant Women and Infants
Nitrate is one of a handful of contaminants where pregnancy and infancy materially change the risk equation. Methemoglobinemia risk peaks in infants under six months whose stomach acid is too weak to suppress nitrate-reducing bacteria. Boiling water concentrates nitrate rather than removing it — the only effective response is to use filtered or bottled water for formula reconstitution. Our pregnant women and water quality guide and baby and infant water safety guide cover this in detail.
What You Can Do
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Check your zip code on EWG’s map. EWG’s interactive nitrate map shows your water system’s nitrate levels alongside the national distribution. Cross-reference with your WaterVerge city page.
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If you’re on a private well, test annually. Nitrate is one of the cheapest tests on a standard well-water panel — typically under $25 — and well users are at higher risk than utility customers. See our well water testing guide. Test more often during planting season (April–June) and after heavy rain.
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Filter if your level is elevated. Standard activated carbon and most pitcher filters do not remove nitrate. The proven removal methods are:
| Method | Nitrate Removal | Best For |
|---|---|---|
| Reverse osmosis | 80–90% | Drinking and cooking water (point-of-use) |
| Anion exchange | 75–90% | Whole-house treatment for affected wells |
| Distillation | 95%+ | Small-volume drinking water |
| Activated carbon | Not effective | Will not remove nitrate |
For RO systems certified to NSF/ANSI 58 (which includes nitrate reduction claims), see our best reverse osmosis systems. For whole-house anion exchange, see our best whole-house water filters.
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Don’t boil. Boiling concentrates nitrate. If your water is high in nitrate, boiling is actively harmful, not protective.
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Know your CCR. Your utility reports nitrate annually in its Consumer Confidence Report. Our guide to reading your CCR walks through what to look for, including the difference between an annual average and the highest single detection.
How WaterVerge Tracks This
WaterVerge integrates SDWIS-reported nitrate data into city pages, flagging detections relative to both the federal 10 mg/L MCL and to lower health-based reference points where applicable. As EWG’s underlying dataset becomes available for cross-referencing, city-level pages will display the EWG-style tiered exposure data alongside violation history. Search your city to see current nitrate levels for your utility and learn whether your service area falls in the agricultural runoff hot zones documented in EWG’s analysis.