Nitrate in drinking water: limits, risks & what to do.
Nitrate is a contaminant that reaches drinking water mainly from fertilizer, manure, and septic systems. The EPA limit (MCL) is 10 mg/L measured as nitrogen. Because high nitrate can harm infants under six months within days, a confirmed exceedance is an acute violation — the water system must notify customers within 24 hours.
Nitrate is one of the few acute contaminants.
An exceedance is not a wait-and-monitor situation — it is a same-day public notice.
- 1 · Sample ≥ 10 mg/L nitrate (as N)
- 2 · Confirmation sample within 24 hours
- 3 · Tier 1 public notice within 24 hours acute — using the required health-effects language
Source: 40 CFR §§ 141.62 · 141.23 · 141.202 · Appendix A/B to Subpart Q
What to do when nitrate is high
Protect infants first
If your water exceeds 10 mg/L nitrate (as N), do not use it to mix infant formula and do not give it to children under six months. Use bottled water or water treated by reverse osmosis for formula until the system confirms the water is safe.
Do not boil to fix it
Boiling does not remove nitrate — it concentrates it as water evaporates, making the level higher. Boiling, standard carbon pitcher filters, and softeners do not reduce nitrate.
What removes nitrate
Reverse osmosis and distillation reduce nitrate at the home point of use; ion exchange and electrodialysis are system-scale methods operators use. For a certified home device, look for NSF/ANSI 58 (reverse osmosis) rated for nitrate/nitrite reduction. Standard carbon filters and softeners do not remove nitrate.
Others who should take care
Pregnant people and adults with certain conditions should follow the same advisory. Most healthy adults are not affected at levels near the limit, but the acute risk to bottle-fed infants is why the standard is strict.
Where nitrate in drinking water comes from
Fertilizer and agriculture
Nitrogen fertilizer applied to crops and lawns leaches into groundwater. Agricultural regions with sandy soils and shallow wells see the highest nitrate — it is the most common cause of exceedances in small groundwater systems.
Manure and septic systems
Animal feeding operations, manure storage, and failing or dense septic systems release nitrogen that converts to nitrate and moves into the aquifer that feeds nearby wells.
Natural deposits
Nitrate also occurs naturally from the breakdown of organic matter in soil. Levels are usually low from this source alone, but it adds to the load from fertilizer and septic.
A nitrate exceedance is acute — it’s a 24-hour notice.
Nitrate and nitrite are the drinking-water contaminants EPA treats as acute. A confirmed MCL exceedance is a Tier 1 public notification under 40 CFR § 141.202: customers within 24 hours, by a method reasonably certain to reach them, carrying the EPA-mandated health-effects language. Systems at or above 5 mg/L also move to quarterly monitoring (§ 141.23).
1water’s CCR agent reports your nitrate results each year, and a public-notification generator with the verbatim Appendix B health-effects language is rolling out — so the right Tier 1 notice is ready the moment a confirmation sample comes back. Tell us your state →
Nitrate in drinking water — common questions
- U.S. EPA — National Primary Drinking Water Regulations, maximum contaminant levels for inorganic contaminants, 40 CFR § 141.62; monitoring, 40 CFR § 141.23.
- U.S. EPA — Public Notification Rule, 40 CFR § 141 Subpart Q (§ 141.201–141.205); nitrate and nitrite are Tier 1 (acute) violations.
- U.S. CDC / U.S. EPA — health effects of nitrate in drinking water (methemoglobinemia in infants).
Keep reading
Arsenic in drinking water: limits, risks & removal
The 0.010 mg/L (10 ppb) EPA limit, why arsenic is a chronic cancer risk, where it comes from, how systems remove it, and the Tier 2 30-day notice an exceedance requires.
Turbidity in drinking water: NTU limits & the SWTR
The 0.3 NTU / 1 NTU Surface Water Treatment Rule limits for filtered surface-water and GWUDI systems, why turbidity shields pathogens from disinfection, and what an exceedance triggers.
The Ground Water Rule: what it requires of ground water systems
How 40 CFR 141 Subpart S protects ground water systems from fecal contamination — sanitary surveys, triggered source-water monitoring after a coliform-positive, and corrective action.
Catch an exceedance before it becomes a rejection.
1water helps small and mid-size water systems stay ahead of nitrate, coliform, lead, PFAS, and CCR requirements — self-serve, and priced for the small end.