At a glance
| Chemical family | Inorganic anion (NO3−); the fully-oxidized, stable form of nitrogen in water. Reduced in the body to nitrite (NO2−), which is the biologically active species. Distinct from dietary nitrate in vegetables, which carries protective co-factors that water nitrate does not. |
| CAS number | 14797-55-8 (nitrate ion); 84145-82-4 and salt-specific CAS for sodium/potassium/calcium nitrate |
| Classification | IARC Group 2A — "ingested nitrate or nitrite under conditions that result in endogenous nitrosation" (Monograph Vol 94, 2010). EPA drinking-water Maximum Contaminant Level 10 mg/L as nitrate-nitrogen (≈ 45 mg/L as nitrate ion). WHO guideline 50 mg/L as nitrate ion. Not classified as carcinogenic on its own outside the nitrosation pathway. |
| Where you encounter it | Drinking water — overwhelmingly private wells in agricultural regions (Midwest Corn Belt, Central Valley of California, parts of the Great Plains, dairy regions). Fertilizer and manure leaching is the dominant source; septic-system effluent is the second. Also present in cured meats (added as a preservative) and, in a different and largely benign context, in leafy-green and root vegetables. |
| Sleep micro environment relevance | Indirect — nitrate is an ingestion exposure, not an air or bedroom exposure. It is on Embr because "the chemistry of where you live" includes the water you drink and mix formula with, and because the water/well audience overlaps heavily with the farm-family and private-well readers the Atlas already serves. |
| Activated carbon capture | Not applicable — nitrate is a dissolved inorganic ion, not a VOC, so activated carbon does not remove it. The validated technologies are reverse osmosis, anion-exchange, and distillation. Inferred from standard water-treatment engineering; carbon adsorption targets organics, not the nitrate anion |
Regulatory & certification status
Where nitrate stands across the major drinking-water systems. Nitrate is regulated as a drinking-water contaminant rather than as a product ingredient, so the rows below are water standards, not textile or foam certifications.
| United States | EPA sets an enforceable Maximum Contaminant Level of 10 mg/L measured as nitrate-nitrogen (equivalent to ~45 mg/L as the nitrate ion) under the Safe Drinking Water Act, with a separate 1 mg/L limit for nitrite. Public water systems must test and treat to meet it; private wells are exempt and are the owner's responsibility. The MCL was set on the basis of preventing infant methemoglobinemia. Regulatory — US EPA |
| European Union | The EU Drinking Water Directive sets a nitrate limit of 50 mg/L (as nitrate ion), matching the WHO guideline. The related Nitrates Directive (91/676/EEC) regulates agricultural nitrogen at the source by designating Nitrate Vulnerable Zones and capping manure/fertilizer application — a source-control approach the US largely lacks. Regulatory — European Commission |
| Canada | Health Canada sets a maximum acceptable concentration of 10 mg/L for nitrate (as nitrogen), consistent with the US figure, under the Guidelines for Canadian Drinking Water Quality. Regulatory — Government of Canada |
| World Health Organization | The WHO Guidelines for Drinking-water Quality set 50 mg/L as nitrate ion (short-term, protective against methemoglobinemia) and note that the guideline is protective for bottle-fed infants, the most sensitive subgroup. WHO explicitly frames the value around the infant endpoint. Regulatory — WHO |
| International | IARC classifies ingested nitrate/nitrite "under conditions that result in endogenous nitrosation" as Group 2A (probably carcinogenic to humans), Monograph Vol 94 (2010). The classification is conditional on the nitrosation pathway — it is not a blanket statement that all nitrate ingestion is carcinogenic, which is why dietary vegetable nitrate (with its inhibitory co-factors) is treated differently. Regulatory — IARC Monographs Vol. 94 |
| Certifications | For point-of-use treatment, NSF/ANSI 58 (reverse osmosis) and NSF/ANSI 53 include nitrate-reduction claims — verify the specific "nitrate/nitrite reduction" language on the certification, as not every NSF-listed filter carries it. Ion-exchange systems certified to NSF/ANSI 44 (residential softeners) can be configured for nitrate. Industry — NSF |
| The 72-hour test window | Not applicable. Nitrate is a waterborne ingestion exposure with no relationship to the short VOC-emission chamber tests used for mattresses and foam. It is detected by a standard water lab test, not an air-emissions test. Inferred — from the exposure route (ingestion via water) versus the VOC/air focus of product emissions testing |
What it is
Nitrate (NO3−) is the stable, fully-oxidized form of nitrogen dissolved in water. It is highly soluble, does not bind to soil, and moves freely with groundwater — which is exactly why it is the world's most widespread groundwater contaminant. Nitrate itself is relatively inert; the toxicological action comes from its reduction to nitrite (NO2−), which happens both by bacteria in the environment and by bacteria in the human gut. Nitrite is the species that oxidizes hemoglobin and that participates in forming N-nitroso compounds, the class that includes several potent carcinogens.
The dominant source is agriculture. Synthetic nitrogen fertilizer and animal manure are applied to fields in quantities that crops cannot fully take up; the surplus nitrogen is converted to nitrate and leaches down into aquifers, where it can persist and accumulate for decades. Septic systems are the second major source — a rural home on a private well downgradient of its own or a neighbor's septic field is a classic exposure scenario. Because both sources feed groundwater, nitrate is concentrated in private wells and small rural systems, and is comparatively controlled in large municipal supplies that test and treat.
The reason nitrate deserves careful, non-alarmist handling is that the same ion sits in two very different health stories. In drinking water, without the vitamin C and polyphenols that accompany it in vegetables, nitrate feeds endogenous nitrosation and has been linked in cohort studies to colorectal cancer. In vegetables, the same nitrate is generally considered neutral or even beneficial (it supports nitric-oxide signaling and cardiovascular function). Conflating the two — "nitrate is in spinach, so it's fine in water" — is one of the most common ways this topic gets argued badly.
Where you encounter it
From private wells in farm country
This is the exposure that matters. Roughly 40 million-plus Americans rely on private wells that are not subject to the Safe Drinking Water Act's testing and treatment requirements. In the Corn Belt, California's Central Valley, and intensive dairy regions, nitrate routinely exceeds 10 mg/L in shallow wells. Because nitrate leaches with rain and follows fertilizer application, well concentrations can swing seasonally — a well that tested clean in winter can exceed the limit after spring application and a wet May. Annual testing (and re-testing before mixing infant formula) is the core protective action.
From septic systems
Septic effluent is nitrogen-rich, and in areas with dense on-site wastewater and permeable soils, septic contribution to well nitrate can rival agriculture. A household drawing from a shallow well near its own leach field, or in a subdivision of closely-spaced septic lots, has a plausible self-generated exposure independent of any farm.
From cured meats (a separate, dietary route)
Sodium nitrate and sodium nitrite are added to bacon, ham, hot dogs, and other cured meats as preservatives and color fixatives. This is a real nitrite/N-nitroso exposure and part of the reasoning behind the IARC classification of processed meat — but it is a food-additive question handled by food-safety regulation, distinct from the drinking-water pathway this page is about. It is worth naming so the picture is complete.
What the research says
Blue-baby syndrome — the endpoint the limit was built on
Infant methemoglobinemia is the historical and still-valid basis for the nitrate MCL. In infants under about six months, gut chemistry converts more nitrate to nitrite, and fetal hemoglobin is more readily oxidized to methemoglobin, which cannot carry oxygen. The infant becomes cyanotic — literally blue-tinged — and in severe cases the condition is fatal. The CDC guidance is explicit: never mix infant formula with well water that exceeds the nitrate limit, and do not boil it. Regulatory The 10 mg/L limit is genuinely protective for this endpoint.
Colorectal cancer below the limit — the Danish cohort
Schullehner, Hansen, Thygesen, Pedersen and Sigsgaard (2018) in the International Journal of Cancer followed 2.7 million Danes with individual-level, address-matched drinking-water nitrate histories. They found colorectal-cancer risk beginning to rise well below the regulatory limit — statistically significant elevations in the highest exposure groups (cut-points at roughly 3.9 and 9.3 mg/L as nitrate-nitrogen), with about a 15% higher risk in the most-exposed group versus the least. Peer-reviewed The individual-level exposure assignment is what makes this study unusually strong; it is the anchor for the "legal ≠ risk-free" framing.
The broader review — what is and isn't established
Ward, Jones, Brender and colleagues (2018) published an updated review of drinking-water nitrate and human health in IJERPH. It concluded that the strongest epidemiological signal below the regulatory limit is for colorectal cancer, with additional but less consistent evidence for thyroid effects and certain adverse birth outcomes (neural-tube defects, preterm birth) in some studies. Peer-reviewed The honest reading is: the infant endpoint is settled, the colorectal-cancer signal is credible and mechanistically plausible, and the reproductive/thyroid associations are suggestive but not yet firm.
Regulatory reference values
The EPA MCL for nitrate is 10 mg/L as nitrate-nitrogen (≈ 45 mg/L as nitrate ion). Regulatory The WHO guideline is 50 mg/L as nitrate ion. Regulatory The ATSDR Toxicological Profile for Nitrate and Nitrite sets oral minimal risk levels and details the methemoglobinemia mechanism. Regulatory
What helps reduce exposure
Test the well — and re-test before mixing infant formula. Nitrate is a cheap, standard water-lab test. If there is a new baby or a pregnancy in the household, test before relying on the water, because nitrate can spike seasonally after fertilizer application and rain. State health departments and county extension offices list certified labs.
For water above the limit: install reverse osmosis, anion exchange, or distillation. Point-of-use reverse osmosis (NSF/ANSI 58 with a verified nitrate claim) at the kitchen sink is the common, cost-effective fix for drinking and cooking water. Whole-house anion-exchange systems handle higher flow. Verify the specific nitrate-reduction certification.
Use an alternative water source for infants if the well exceeds the limit. Bottled water certified low in nitrate, or treated water, for formula preparation until the well is remediated.
For chronic exceedance, address the source where possible. Wellhead protection, correct septic maintenance and setback, and (at the community scale) source-water nitrogen management reduce the input rather than just filtering the output.
What does NOT help
- Boiling. This is the dangerous one. Boiling concentrates nitrate as water evaporates — it raises the dose, and a caregiver boiling water to make it "safe" for an infant is doing the opposite.
- Standard carbon pitcher and faucet filters. Activated carbon targets organic compounds and chlorine taste/odor; it does not remove the dissolved nitrate ion. A "filtered water" claim without a specific nitrate certification is not protective for nitrate.
- Water softeners (as normally configured). A conventional cation-exchange softener removes hardness minerals, not nitrate, unless specifically set up with a nitrate-selective anion resin.
- Letting water sit or aerating it. Nitrate is stable and dissolved; it does not off-gas or settle out.
- Reasoning from vegetables. "Nitrate is in spinach so it's fine" ignores that water nitrate lacks the vitamin C and polyphenols that make vegetable nitrate behave differently — and it is water nitrate the cancer cohorts implicate.
Open research questions
- The shape of the colorectal-cancer dose-response below the current MCL — the Danish cohort establishes a signal, but the precise threshold (if any) and the generalizability to US populations with different diets and co-exposures is still being characterized. Speculation re: exact sub-MCL threshold; the association itself is peer-reviewed
- Reproductive and thyroid endpoints — associations with neural-tube defects, preterm birth, and thyroid function appear in some studies but not consistently; whether these reflect causal effects at typical exposures is unresolved. Speculation
- Dietary modifiers — whether vitamin C intake or overall diet meaningfully blunts the water-nitrate cancer risk in exposed populations is biologically plausible but not established at the population level. Speculation
- Whether the US MCL should be lowered to reflect the sub-limit cancer evidence — a policy and cost-benefit question that sits beyond the toxicology and remains actively debated. Inferred from the drinking-water policy literature
Where you meet Nitrate across your home
The same compound turns up in more than one place you live. Here's where it shows up in Embr — each links to the full breakdown for that part of your home.
Citations
- US Environmental Protection Agency. National Primary Drinking Water Regulations — Nitrate Maximum Contaminant Level 10 mg/L (as nitrogen). epa.gov Regulatory
- World Health Organization (2016). Nitrate and nitrite in drinking-water — Background document for the WHO Guidelines for Drinking-water Quality. Guideline value 50 mg/L nitrate. who.int Regulatory
- International Agency for Research on Cancer (2010). IARC Monographs Volume 94: Ingested Nitrate and Nitrite, and Cyanobacterial Peptide Toxins — Group 2A under endogenous-nitrosation conditions. Lyon: IARC. publications.iarc.fr Regulatory
- Agency for Toxic Substances and Disease Registry (2017). Toxicological Profile for Nitrate and Nitrite. atsdr.cdc.gov Regulatory
- Schullehner J, Hansen B, Thygesen M, Pedersen CB, Sigsgaard T (2018). Nitrate in drinking water and colorectal cancer risk: A nationwide population-based cohort study. International Journal of Cancer, 143(1):73-79. DOI 10.1002/ijc.31306 Peer-reviewed
- Ward MH, Jones RR, Brender JD, de Kok TM, Weyer PJ, Nolan BT, Villanueva CM, van Breda SG (2018). Drinking Water Nitrate and Human Health: An Updated Review. International Journal of Environmental Research and Public Health, 15(7):1557. DOI 10.3390/ijerph15071557 Peer-reviewed
- US Centers for Disease Control and Prevention. Nitrate in drinking water — methemoglobinemia ("blue baby syndrome") and private-well guidance. cdc.gov Regulatory
Frequently asked questions
What is a safe level of nitrate in drinking water?
The US EPA legal limit (Maximum Contaminant Level) is 10 mg/L measured as nitrate-nitrogen, equivalent to about 45 mg/L measured as the nitrate ion. The WHO guideline is 50 mg/L as nitrate ion. That limit was set decades ago to prevent blue-baby syndrome in infants, and it does that job. What it was not designed for is the more recent finding that colorectal-cancer risk begins to rise at nitrate levels well below the limit — around 4 mg/L in the largest study. So "legal" and "zero added risk" are not the same number here, and that gap is the honest headline.
Where does nitrate in tap water come from?
Overwhelmingly from agriculture — synthetic nitrogen fertilizer and animal manure applied to fields leach into groundwater. Septic-system effluent is the second major source, which matters for rural homes on both a private well and a septic field. Because these are groundwater sources, private wells in farm country are far more likely to exceed the limit than large municipal systems, which are tested and treated. Nitrate is also colorless, odorless, and tasteless, so you cannot detect it without a test.
Does boiling water remove nitrate?
No — boiling makes nitrate worse. As water evaporates, the nitrate stays behind and concentrates in the smaller remaining volume. This is the single most dangerous misconception about nitrate, because a parent trying to make water safer for an infant by boiling it is actually raising the dose. Nitrate is removed by reverse osmosis, ion exchange (anion) systems, or distillation — not by boiling, and not by standard carbon pitcher filters.
Why is nitrate dangerous for babies but not adults?
Infants under about six months have a specific vulnerability: gut bacteria more readily convert nitrate to nitrite, and infant (fetal) hemoglobin is more easily oxidized by nitrite into methemoglobin, which cannot carry oxygen. The result is methemoglobinemia, or "blue baby syndrome" — the baby's skin takes on a bluish tint from oxygen starvation. This is an acute, potentially fatal condition. Never use well water above the nitrate limit to mix infant formula, and do not boil it to try to fix it.
Should I test my well for nitrate?
Yes, especially if you are in an agricultural area, on a septic system, or have an infant or pregnant person in the household. Private wells are not covered by the EPA testing requirements that apply to public water systems, so the responsibility is entirely the owner's. Nitrate can change seasonally — it often spikes after fertilizer application and heavy rain — so test at least annually, and test before mixing infant formula if you have a new baby. State health departments and county extension offices list certified laboratories, and nitrate is a cheap, standard test.
Is nitrate in vegetables the same as nitrate in water?
Chemically it is the same ion, but the health context differs. Most dietary nitrate comes from vegetables (leafy greens, beets), and that intake is generally regarded as beneficial or neutral because vegetables also carry vitamin C and polyphenols that inhibit the formation of carcinogenic N-nitroso compounds. Nitrate in drinking water arrives without those co-factors, and it is the water-nitrate exposure — not vegetable nitrate — that the colorectal-cancer cohort studies have linked to elevated risk. This is why "nitrate is in spinach, so water nitrate is fine" is a flawed comparison.
Related compounds
Embr researches the chemistry of where you live — including the water you drink. See the methodology page for how this Atlas tags claims by evidence strength, and the tap-water source hub for how nitrate fits alongside the other things in your water. For rural and well-water context, see farm family sleep.
Last reviewed 2026-07-12. If you find a factual error, contact us.