Nitrate

At a glance: Nitrate is a nitrogen compound from fertilizer, septic systems and animal waste that seeps into groundwater, especially shallow wells. Above EPA’s limit of 10 mg/L (as nitrogen), it can make infants under six months seriously ill by interfering with how their blood carries oxygen. Test your well every year and before a baby drinks the water or formula made with it. Boiling makes it worse. A reverse osmosis unit certified for nitrate at the kitchen tap is the usual fix.

Public water systems must meet the 10 mg/L limit. Nitrate is mostly a private well issue.

What it is and where it comes from

The Minnesota Department of Health names the sources: fertilizers used on crops, yards, gardens and golf courses, discharge from sewage systems, and animal waste. EPA’s health table lists runoff from fertilizer use and leaking septic tanks. Nitrate dissolves easily and moves with water down into aquifers.

Some wells are more exposed than others. MDH says shallow wells and wells in sand, karst and fractured rock aquifers are particularly vulnerable. EPA’s guidance for private wells lists nitrate among the tests to add if your well is near farms or orchards.

It is one of the most common health problems in domestic wells. A USGS study of more than 2,000 domestic wells found nitrate above the EPA limit in roughly 5 to 7 percent of them.

Health and household effects

Nitrate is a health issue with no household signs: it has no color, taste or smell at levels that matter.

The main risk is to infants. EPA says infants below six months who drink water with nitrate above the limit could become seriously ill and may die. MDH explains that too much nitrate “can affect how blood carries oxygen and cause methemoglobinemia (also known as a blue baby syndrome).”

Nitrate is also a marker. MDH notes that nitrate above 1 mg/L in well water suggests additional testing may be a good idea.

Limits and what they mean

Standard	Level	What it means
EPA MCL and health goal, nitrate	10 mg/L as nitrogen	Enforceable limit for public systems; protects infants
EPA MCL and health goal, nitrite	1 mg/L as nitrogen	Separate limit for nitrite
WHO guideline, nitrate	50 mg/L as nitrate (about 11 as nitrogen)	Protects bottle-fed infants
MDH marker for more testing	1 mg/L	MDH suggests additional testing above this level

Check the units on your lab report. “Nitrate as N” or “nitrate-nitrogen” is compared with EPA’s 10 mg/L. “Nitrate as NO3” uses a different scale, where 10 mg/L as nitrogen equals about 44 mg/L.

EPA’s health goal equals its enforceable limit for nitrate, 10 mg/L. Private wells are not covered by the rule, so the owner decides what to do with a result.

How to test

Use a state-certified lab. Wisconsin’s state lab charges $35 for nitrate and Penn State includes it in its $70 package with coliform bacteria, pH and TDS. MDH says to test for nitrate every year, and the CDC and EPA both include it in the annual well test.

Test again right away if you are pregnant, a baby is coming, or there has been flooding or land disturbance near the well, as the CDC advises. Our well testing guide covers labs and sampling.

Treatment options

Method	How well it works	Certification to look for	Cost range
Reverse osmosis, point of use	High	NSF/ANSI 58, nitrate/nitrite reduction	$300 to $1,500
Distillation, point of use	High	NSF/ANSI 62	$300 to $1,200
Nitrate-selective anion exchange (specialty media), whole house	High if maintained	None common; resins may be certified (MDH)	$1,500 to $2,500
Water softener	Not effective	Not applicable	Not a nitrate fix
Activated carbon	Not effective	Not applicable	Not a nitrate fix
Boiling	Makes it worse	Not applicable	Not applicable

Cost ranges are Minnesota Department of Health estimates based on 2017 and 2018 quotes, low end self-installed and high end professionally installed.

Point of use is usually right. Nitrate matters for what you drink and mix into formula, so a certified RO unit at the kitchen tap covers the risk for far less than whole-house treatment. Wisconsin’s health department lists reverse osmosis certified to NSF/ANSI 58 as the device for nitrate. See whole-house filter vs reverse osmosis, and use the filter finder to check which RO systems list a nitrate claim.

Anion exchange has trade-offs. MDH notes it can make water more corrosive, a concern with copper or lead plumbing, and if not maintained it can release a high concentration of the contaminant back into the water.

When to call a professional

Call your county or state health department if nitrate is above 10 mg/L, and use bottled water for infant formula until the water is treated and retested.

Call a licensed well contractor if levels are high or rising, to check whether the well’s construction or depth is part of the problem. Wisconsin’s health department notes that drilling a new well is another option for a contaminated private well. If you choose whole-house anion exchange, have a water treatment professional size it and set up maintenance, and test for lead and copper afterward.