Nitrate in well water
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private wells tested in Holt County, Missouri had nitrate above the limit, the highest share of any county, according to Missouri DHSS private well sampling summaries.
Nitrate reaches wells from fertilizer, septic systems and manure. Above the limit it can cause methemoglobinemia (blue baby syndrome) in infants under six months, and long-term exposure is associated with some cancers. Shallow and dug wells near farmland or dense septic systems are most at risk.
- EPA limit
- 10 mg/L (EPA MCL as nitrogen (40 CFR 141.62))
- Missouri level
- 10 mg/L
- CAS number
- 14797-55-8
Check your nitrate number
Type the value from your lab report. It is compared to the EPA limit, the same way the full interpretation does it.
Test your own well for nitrate
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
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Systems that remove nitrate
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Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For nitrate
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For nitrate
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
Rather have it installed and sized for your well? Book a free in-home water test with a licensed local company.
Where nitrate is worst, by homeowner tests
Counties ranked by the share of private wells above the state guidance level in tests homeowners sent to the state lab. Shares combine town summaries, weighted by wells tested.
| County | Above state level | Wells tested | Highest |
|---|---|---|---|
| Holt County, Missouri | 32 | ||
| Nodaway County, Missouri | 129 | ||
| Lancaster County, Pennsylvania | 403 | 30.1 mg/L | |
| Rock County, Wisconsin | 2,220 | 64.4 mg/L | |
| Portage County, Wisconsin | 3,842 | 76 mg/L | |
| Trempealeau County, Wisconsin | 894 | 48.2 mg/L | |
| Blair County, Pennsylvania | 81 | 73.4 mg/L | |
| Green Lake County, Wisconsin | 1,317 | 52.1 mg/L | |
| Pepin County, Wisconsin | 390 | 39.5 mg/L | |
| Columbia County, Wisconsin | 2,862 | 48.1 mg/L | |
| Dane County, Wisconsin | 7,299 | 127 mg/L | |
| Franklin County, Pennsylvania | 119 | 15.4 mg/L | |
| Dunn County, Wisconsin | 1,265 | 45.4 mg/L | |
| Clark County, Missouri | 87 | ||
| Green County, Wisconsin | 2,533 | 69.9 mg/L |
By individual samples
Counties with at least 30 individual samples in public monitoring data, against the EPA limit.
| County | Above EPA limit | Samples | Detected | Median |
|---|---|---|---|---|
| Lynn County, Texas | 42 | 100% | 19.8 mg/L | |
| Knox County, Texas | 127 | 97% | 17.2 mg/L | |
| Neosho County, Kansas | 43 | 100% | 28 mg/L | |
| Navarro County, Texas | 34 | 94% | 29 mg/L | |
| Osage County, Kansas | 40 | 100% | 49.4 mg/L | |
| Anderson County, Kansas | 40 | 100% | 21 mg/L | |
| Major County, Oklahoma | 1,286 | 100% | 13.5 mg/L | |
| Harper County, Oklahoma | 601 | 100% | 14 mg/L | |
| Malheur County, Oregon | 452 | 100% | 13 mg/L | |
| Lancaster County, Pennsylvania | 4,942 | 98% | 12 mg/L | |
| Merrick County, Nebraska | 794 | 94% | 13.5 mg/L | |
| Brown County, Kansas | 141 | 100% | 14.7 mg/L | |
| Tom Green County, Texas | 82 | 98% | 21 mg/L | |
| Morris County, Kansas | 48 | 100% | 12 mg/L | |
| Kingfisher County, Oklahoma | 1,127 | 100% | 12 mg/L |
How to test
Use a state-certified lab and a proper sampling bottle; hardware-store strips cannot measure nitrate at the levels that matter. Collect from the kitchen tap before any treatment, and again after treatment if you install it.
How to treat
- Point-of-use reverse osmosis
- Anion exchange
- Distillation
Analysis: Nitrate in private wells, decade by decade, from the same public records.