Nitrate is one of the few well-water results that comes with a clear federal number, and one of the easiest to treat the wrong way. You can’t see, smell, or taste it, a water softener doesn’t touch it, and boiling makes it worse. This guide explains how to read a nitrate result, what the Minnesota Department of Health tells well owners to do first, how reverse osmosis and anion exchange compare, and what NSF’s own listings show about nitrate claims (checked Oct 28, 2026). Specs and prices come from official pages with the date we checked them, our math is labeled as ours, and we haven’t tested any of these systems.
This isn’t health advice. What a nitrate result means for your household, especially if anyone pregnant or an infant uses the water, is a question for your doctor and your local or state health department. We quote what health agencies say; we don’t add to it.
The short answer
- Test every year with an accredited or state-certified lab. Results are usually reported as nitrate “as N” (nitrogen). The federal limit is 10 mg/L as N.
- Above 10 mg/L, the Minnesota Department of Health’s first steps aren’t equipment: use another source of drinking water such as bottled water, keep babies under six months off the well water, don’t boil it, have a licensed well contractor inspect the well, and look for nitrate sources near it.
- A softener, a carbon filter, a sediment filter, and UV don’t reduce nitrate. The common options are reverse osmosis at the kitchen sink, anion exchange for the whole house, or distillation.
- “NSF/ANSI 58 certified” isn’t the same as nitrate certified. Only some RO listings carry a “Nitrate/Nitrite Reduction” claim. On Oct 28, 2026, 27 of the 56 companies on NSF’s 58 listing had that claim on at least one model.
- The certified claim has limits: water with no more than 27 mg/L nitrate plus 3 mg/L nitrite (as N), at 40 psi or more of water pressure. Many wells run below 40 psi part of the time.
- Test the treated water, at the tap you drink from, after installation and on a schedule.
Reading a nitrate result
The EPA’s National Primary Drinking Water Regulations (checked Oct 28, 2026) set the maximum contaminant level for nitrate at 10 mg/L measured as nitrogen and for nitrite at 1 mg/L as nitrogen. The EPA’s table lists the sources as fertilizer runoff, septic tanks and sewage, and natural deposits. Public water systems have to meet those limits. Private wells don’t, so the testing is up to you.
Watch the units. The Water Quality Association’s nitrate/nitrite fact sheet (checked Oct 28, 2026) notes that 10 mg/L as nitrogen is the same as 44.2 mg/L measured as the nitrate ion (NO₃). A lab report that says “nitrate 30 mg/L” could mean either, and the difference is more than fourfold. If the report doesn’t say “as N” or “NO₃-N,” ask the lab. One mg/L is the same as one part per million (ppm).
What the Minnesota Department of Health (MDH) says about the numbers, from its Nitrate in Well Water and Nitrate in Drinking Water pages (both checked Oct 28, 2026):
- Natural nitrate in Minnesota groundwater is usually below 1 mg/L. Above 1 mg/L, MDH says additional testing “may be a good idea,” because “if nitrate is present, then other contaminants such as pesticides may be as well.”
- 3 mg/L is below the federal standard, but MDH says it “suggests human-made sources of nitrate have contaminated the water and the level could increase over time.” About 4% of Minnesota wells built since 1991 are above 3 mg/L.
- Above 10 mg/L, MDH lists the steps below. The Minnesota Department of Agriculture’s township testing found more than 10% of sampled private wells above 10 mg/L in some townships.
MDH describes the wells most vulnerable to nitrate as shallow wells, wells in sand, karst, and fractured-rock aquifers, dug wells without watertight casings, and wells with damaged casings or fittings. Nitrate levels can change, so one good result doesn’t settle it: MDH recommends a nitrate test every year, and also before a pregnancy or before an infant will use the water.
Where to test: In Minnesota, MDH keeps a list of accredited labs that accept samples from private well owners. Elsewhere, ask your state or county health department for state-certified labs. Our guide to finding your water hardness covers the EPA’s yearly well-test list (coliform bacteria, nitrate, total dissolved solids, and pH). If you’re on city water, nitrate is one of the results in your utility’s Consumer Confidence Report, and the utility has to meet the 10 mg/L limit.
What MDH says to do above 10 mg/L
From MDH’s well-water page (checked Oct 28, 2026), in order:
- Get drinking water from a safe alternative source, such as bottled water.
- Make sure babies under six months old don’t drink the well water.
- Don’t boil the water to remove nitrate. MDH: “Boiling will make nitrate more concentrated.”
- Have a licensed well contractor inspect the well.
- Find and get rid of potential nitrate sources (fertilizer, septic systems, animal waste) near the well.
MDH calls home water treatment “also an option,” and encourages fixing sources and repairing the well first. It adds a caution that matters for anyone buying equipment: “Even with home water treatment, MDH recommends that no babies under six months old drink the water (a safety precaution in the event the water treatment fails).” The health details, including who is at higher risk, are on MDH’s pages; ask your doctor or local health department what your result means for your household.
What doesn’t remove nitrate
Nitrate dissolves completely and carries a negative charge, so equipment that catches particles, adsorbs chemicals, or swaps positively charged minerals doesn’t remove it:
- Water softeners. A softener (NSF/ANSI 44) exchanges calcium and magnesium, which are positively charged. Nitrate isn’t. US Water Systems makes the same point from the other side on its nitrate system page: “while it looks like a water softener it doesn’t serve as one.”
- Carbon filters (including whole-house carbon for chloramine) and sediment filters. MDH’s Home Water Treatment fact sheet (checked Oct 28, 2026) doesn’t list nitrate among what carbon filters are designed to remove.
- UV. UV targets microorganisms only (see our UV guide).
- Boiling. It concentrates nitrate, per MDH.
NSF’s listings line up with this. On Oct 28, 2026, we found no “Nitrate” claims on NSF’s NSF/ANSI 53 (health-effect filters) or NSF/ANSI 44 (softeners) listings, and NSF’s NSF/ANSI 62 (distillation) listing showed “No Matching Products Found.” The nitrate claims we found were all on the reverse osmosis listing.
The three options that do
MDH’s Home Water Treatment fact sheet lists nitrate among what these are designed to fully or partially remove. Its cost ranges are MDH’s estimates “based on quotes obtained in 2017 and research in 2018,” so treat them as rough:
| Option | Where it goes | MDH cost estimate (2017-18) | Main trade-offs (MDH) |
|---|---|---|---|
| Reverse osmosis (RO) | Usually one kitchen tap (point of use) | $300 to $1,500 to buy; $100 to $200 every 1 to 2 years | Wastewater; may need pre-treatment so the membrane doesn’t clog |
| Whole-house RO | Whole house | $5,000 to $12,000; $250 to $500 every 1 to 2 years | Same, at a much larger scale |
| Anion exchange | Whole house (MDH lists no point-of-use version) | $1,500 to $2,500; $700 to $900 every 8 to 10 years | Uses salt; can make water more corrosive; poorly maintained units can dump contaminants back into the water |
| Distillation | Point of use (MDH lists no whole-house version) | $300 to $1,200, plus the energy to boil water | Heating is expensive; water may taste “flat” |
Since nitrate matters for water you drink and cook with, a single RO system at the kitchen sink is the common answer. Whole-house treatment makes more sense if every tap in the house is used for drinking, or a health professional advises it.
Reverse osmosis: reading an NSF/ANSI 58 nitrate claim
We read NSF’s full NSF/ANSI 58 listing (“current as of Wednesday, October 28, 2026”). The certified claims vary by model, and “Nitrate/Nitrite Reduction” is a separate claim that many certified RO systems don’t have:
- 27 of the 56 companies listed had the nitrate claim on at least one model.
- Several well-known RO brands are listed under NSF/ANSI 58 without a nitrate claim, including iSpring (lead, fluoride, TDS, and other claims, but no nitrate), Express Water (TDS only), and EcoWater (many claims, no nitrate) as of Oct 28.
- US Water Systems doesn’t appear on the NSF/ANSI 58 listing, so its RO systems aren’t NSF-certified for nitrate as systems. More on that below.
A certified nitrate claim comes with conditions that are printed on the system’s performance data sheet. A.O. Smith’s AORO-50, which NSF lists with the nitrate claim, is one example. Its performance data sheet (dealer-hosted copy, checked Oct 28, 2026) says the system “is acceptable for treatment of influent concentrations of no more than 27 mg/L nitrate and 3 mg/L nitrite in combination measured as N and is certified for nitrate/nitrite reduction only for water supplies with a pressure of 280 kPa (40 psig) or greater.” The test water was 27 mg/L nitrate plus 3 mg/L nitrite as N, the treated water had to come out at or below 10 mg/L, and the sheet lists 70% nitrate reduction. It also says water that exceeds its limits for hardness, iron, manganese, and hydrogen sulfide needs pre-treatment.
Three practical things follow:
1. Know your number before you buy. If your well tests above 30 mg/L combined nitrate and nitrite as N, you’re outside what the certification test covered. Our math, as an illustration only: a system that removes 70% would bring 20 mg/L down to about 6 mg/L, but 40 mg/L only to about 12 mg/L, which is still above the limit. Real performance varies with the membrane, temperature, and pressure, so treat this as a reason to test, not a prediction.
2. Check your well pressure. The certified claim needs 40 psi or more. Many wells don’t hold that all the time: a pressure switch set to 30/50 turns the pump on at 30 psi and off at 50 psi (Amtrol’s Well-X-Trol manual uses 30/50 as its example setting, checked Oct 28, 2026). Look at the gauge on your pressure tank while water is running. If it drops below 40 psi, ask the RO seller or a licensed contractor whether you need a booster pump or a different pressure setting.
3. Pre-treat for the rest of your water. RO membranes are sensitive to hardness, iron, manganese, and sulfur. If your well needs a softener (size it with our calculator) or an iron filter anyway, those go upstream of the RO.
Whole-house anion exchange
An anion exchange system looks like a softener and also regenerates with salt, but its resin swaps nitrate (and other negatively charged ions) for chloride. Two things matter more here than with a softener.
Sulfate competes with nitrate. The UK Drinking Water Inspectorate’s treatment guide (checked Oct 28, 2026) explains that “conventional anion exchange resins have a higher affinity for sulphate than for nitrate,” and that “nitrate selective resins, which give better uptake of nitrate in the presence of sulphate,” are preferred. Purolite’s nitrate removal application guide (checked Oct 28, 2026) describes the risk: if a unit runs past its capacity, or the household doesn’t keep the salt topped up, sulfate can push nitrate off the resin, and “the nitrate concentration in the treated water exceeds that in the raw water.” That’s called nitrate dumping. Purolite rates nitrate-selective resin “best” for avoiding it and recommends nitrate-selective resin for water with a high sulfate-to-nitrate ratio. So get sulfate on your lab test too, and ask what resin a system uses.
Order matters. Purolite says that if softening is also being done, “the softener should be placed upstream of the nitrate treatment,” and that the water should ideally have no chlorine going in. Its guide also notes some resin types can give off a mild fishy odor when new, which it describes as an aesthetic issue, not a health one.
No NSF system certification to lean on. We found no nitrate claims on NSF’s 44 or 53 listings (Oct 28, 2026), so for whole-house anion exchange you’re relying on the resin maker’s data, the seller’s sizing, a proper regeneration setup, and your own follow-up tests. MDH’s fact sheet says anion “resins may be certified” for nitrate; ask the seller for the resin’s certification and check it with the certifier.
What US Water Systems sells for nitrate
Prices and specs from the official product pages (checked Oct 28, 2026); US Water Systems shows these as marked down from a higher listed price, and its sale pricing may change after Oct 31. Claims are the seller’s own.
| Product | Price | What the seller says |
|---|---|---|
| Matrixx Nitrate Removal System 7 GPM / 15 GPM | $1,706.36 / $2,066.36 | 1.0 / 2.0 cu ft resin, 7 / 15 gpm max flow; salt-regenerated; “not a water softener” |
| Aquapurion 5-Stage RO with Enhanced Nitrate Removal | $479.95 ($579.95 with permeate pump) | Under-sink RO with a dedicated nitrate cartridge as stage 3, 4.5-gallon tank |
| Nitrate Removal Cartridge 2.5” x 10” (USWF-2510-NT) | $41.95 | “Nitrate Selective Anion Resin,” suggested flow 0.1 gpm, fits standard 2.5” x 10” housings |
What to know before buying from this line, as of Oct 28, 2026:
- None of these appear on NSF’s listings. US Water Systems isn’t on the NSF/ANSI 58 listing, and NSF lists no certified US Water Systems softener systems either (only NSF/ANSI 42 filter components), which matches what we’ve found for its other equipment. The pages say they use “NSF Certified components,” which isn’t the same as a system certified for nitrate reduction.
- The Matrixx Nitrate page doesn’t say whether its resin is nitrate-selective. It says “high efficiency resin.” If your water has sulfate, ask before buying. US Water Systems sells ResinTech SIR-100-HP as a nitrate-selective resin and describes it as eliminating nitrate dumping (seller claim).
- The Aquapurion nitrate RO’s own “removes or reduces” list doesn’t include nitrate, even though stage 3 is described as a nitrate filter. Its replacement 3-stage nitrate filter pack ($69.95, checked Oct 28) suggests replacement every 6 months depending on water quality.
If you want a system with a third-party nitrate claim, look for a model with “Nitrate/Nitrite Reduction” on NSF’s own 58 listing and read its performance data sheet. SpringWell, the other seller we cover, showed no nitrate products in a site search on Oct 28, 2026.
After it’s installed
MDH’s general advice for any home treatment (Home Water Treatment fact sheet, checked Oct 28, 2026): “After installing treatment, test the treated water to make sure the treatment is working,” then follow the maker’s maintenance schedule, because “water treatment units that are not properly maintained will lose their effectiveness over time.” For nitrate in particular:
- Test the treated water at the tap you drink from, not just the well.
- Keep testing the raw well water every year. If the nitrate level climbs, a system sized for the old number may not keep up.
- For anion exchange, keep the salt topped up and don’t run it past its metered capacity. Those are the conditions Purolite links to nitrate dumping.
- For RO, change the cartridges and membrane on the maker’s schedule.
Bottom line
- Test yearly at a certified lab, check that the result is “as N,” and add sulfate, coliform bacteria, and the other tests your health department suggests. Arsenic is another common well test with its own treatment rules; see our arsenic guide.
- Above 10 mg/L, start where MDH starts: another drinking-water source, no well water for babies under six months, no boiling, a well inspection, and source removal.
- Softeners, carbon, sediment filters, and UV don’t reduce nitrate. RO at the kitchen tap is the common fix; whole-house anion exchange needs the right resin and steady maintenance.
- “NSF/ANSI 58” alone isn’t enough. Look for “Nitrate/Nitrite Reduction” on NSF’s listing for the exact model, and check that your water stays under 30 mg/L combined and above 40 psi.
For any health question about nitrate, start with your local or state health department and your doctor. For city water, the nitrate result is in your utility’s Consumer Confidence Report; for a well, it takes a lab test.