Utah Private Well Water Risk: Arsenic & Nitrate
These figures are USGS statistical estimates for private (domestic) wells in Utah. They describe the area's modeled risk — not any single well.
Quick answer: Yes — arsenic occurs naturally in Utah groundwater. USGS modeling estimates about 2,132 Utah residents rely on private wells with arsenic above the EPA limit of 10 µg/L. The highest modeled exposure is in Cache County (~602), San Juan County (~286), Millard County (~285). For nitrate, about 0.2% of Utah's ~79,300 private-well residents are modeled above the 10 mg/L limit. These are area estimates, not a test of your well — arsenic has no taste or smell, so only a certified lab test tells you your level.
This is a modeled probability for the area, not a measurement of your well. USGS statistical models estimate how many private wells in this area are likely to exceed the federal limit — they cannot tell you what is in your water. Two neighbors can have very different results. The only way to know your well is to test it.
Nitrate
0.2%
of the private-well population is modeled above the 10 mg/L nitrate limit
~168
people on wells estimated above the limit
~79,300
total residents on private wells statewide
Source: USGS machine-learning nitrate model, Ransom et al. (2022), domestic-well depth zone.
Find out what's actually in your well
USGS models flag arsenic in Utah, but two wells on the same road can test very differently. Arsenic, nitrate and coliform bacteria are the three most common private-well problems, and none of them has a taste or smell. A certified lab test checks all of them at once; the CDC and EPA recommend testing every well at least once a year.
Basic screening only. Confirm arsenic, nitrate and bacteria with a certified lab.
Find a certified drinking-water labAmazon links are affiliate links — we may earn a commission at no extra cost to you.
Arsenic
Across Utah, an estimated ~2,132 people rely on private wells with modeled arsenic above the 10 µg/L EPA limit. The highest modeled exposure is in Cache County (~602 people).
Counties with the highest modeled arsenic exposure
| County | Est. well residents over arsenic limit | 90% range |
|---|---|---|
| Cache County | ~602 | 453–773 |
| San Juan County | ~286 | 217–374 |
| Millard County | ~285 | 221–360 |
| Utah County | ~226 | 165–304 |
| Tooele County | ~196 | 133–285 |
| Box Elder County | ~140 | 101–185 |
23 additional Utah counties have lower modeled arsenic exposure (fewer than 100 estimated well residents over the limit). Of these, 19 have measured USGS well samples: Beaver, Carbon, Davis, Duchesne, Garfield, Grand, Iron, Juab, Kane, Piute, Salt Lake, Sanpete, Sevier, Summit, Uintah, Wasatch, Washington, Wayne, Weber.
Source: USGS domestic-well arsenic model, Lombard et al. (2021); county population product (2017).
Measured well tests by county
The USGS has published laboratory results from wells in 25 Utah counties (at least 5 wells each). These are real measurements of other wells — domestic, public-supply and monitoring wells — not a test of yours. The tables rank counties by the share of sampled wells over each federal threshold.
Nitrate (as N): counties with the most wells > 10 mg/L (EPA MCL)
| County | Wells over | Median | Sampled |
|---|---|---|---|
| Box Elder County | 10% | 1.9 mg/L | 48 wells |
| Millard County | 8% | 1.5 mg/L | 65 wells |
| Utah County | 7% | 1 mg/L | 103 wells |
| Uintah County | 7% | 0 mg/L | 44 wells |
| Beaver County | 7% | 2.3 mg/L | 42 wells |
| Kane County | 7% | 1.3 mg/L | 15 wells |
| Davis County | 7% | 0 mg/L | 14 wells |
| Sanpete County | 5% | 2.7 mg/L | 19 wells |
| Iron County | 4% | 1.5 mg/L | 107 wells |
| Washington County | 4% | 0.8 mg/L | 70 wells |
Manganese: counties with the most wells > 300 µg/L (EPA health advisory)
| County | Wells over | Median | Sampled |
|---|---|---|---|
| Uintah County | 48% | 226 µg/L | 21 wells |
| San Juan County | 9% | 18 µg/L | 47 wells |
| Summit County | 8% | 3 µg/L | 51 wells |
| Salt Lake County | 6% | 5 µg/L | 175 wells |
| Sevier County | 6% | 2 µg/L | 47 wells |
| Utah County | 5% | 1 µg/L | 115 wells |
| Davis County | 5% | 46 µg/L | 19 wells |
| Tooele County | 3% | 3 µg/L | 184 wells |
| Millard County | 3% | 1 µg/L | 67 wells |
| Washington County | 3% | 1 µg/L | 58 wells |
Source: USGS ScienceBase 5f36baa782cee144fb3873e8 (manganese, pH, arsenic) and McMahon et al. (2019), Environ. Sci. Technol. 53:29–38 (nitrate, iron); aggregated by county with Census 2020 boundaries. USGS well samples; not a test of your well.
Match the filter to your test result
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Utah well water: FAQ
Is there arsenic in well water in Utah?
Yes. USGS modeling estimates about 2,132 people in Utah use private wells with arsenic above 10 µg/L, across 29 modeled counties. Arsenic comes from natural bedrock and varies well to well, even between neighbors, so a lab test is the only way to know your own level.
Which Utah counties have the most arsenic in well water?
By modeled number of well residents over the arsenic limit: Cache County (~602), San Juan County (~286), Millard County (~285). Counties with more private-well users rank higher, so a smaller county can still have a high share of affected wells.
How do I remove arsenic from well water in Utah?
Test first. If arsenic is present, a point-of-use reverse-osmosis system under the kitchen sink removes 90%+ of it; boiling does not remove arsenic (it concentrates it), and carbon pitchers and water softeners do not remove it either. Whole-house adsorptive arsenic media is used when levels are high. Re-test after installing and then annually.
Is nitrate a problem in Utah well water?
USGS models about 0.2% of Utah's private-well population (~168 people) above the 10 mg/L nitrate limit. Nitrate is highest in shallow wells near fertilized cropland, septic systems or livestock, and matters most for infants and pregnancy.
Do I need an acid neutralizer for my well in Utah?
Acidic well water is uncommon in Utah, but it does occur. In USGS lab results from 1,723 wells across 24 Utah counties, 2% had pH below 6.5. The most acidic sampled counties are Summit County (9% of 66 wells), Uintah County (9% of 47 wells), Tooele County (4% of 269 wells). You only need a neutralizer if your own well tests below about 6.5 — signs include blue-green stains on fixtures and pinhole leaks in copper pipe. A calcite (or calcite/Corosex) neutralizer tank handles mildly acidic water (roughly pH 6–6.5); very acidic water usually needs soda-ash injection. Test first-draw lead and copper too, since acidic water dissolves both from plumbing.
High manganese in Utah well water — what should I do?
In USGS lab results from 1,232 wells across 24 Utah counties, 4% were above the EPA's 300 µg/L health advisory for manganese and 16% were above the 50 µg/L level where it stains fixtures and laundry black or brown. Sampled counties with the highest share over the health advisory: Uintah County (48% of 21 wells), San Juan County (9% of 47 wells), Summit County (8% of 51 wells). If your own test is over 300 µg/L, don't use the water for infant formula and use another source for drinking and cooking until it is treated — high manganese is linked to neurological effects, especially in babies and children. Boiling does not remove it. For the whole house, an oxidizing filter (greensand, Birm or air-injection) handles manganese, usually alongside iron; a water softener can remove low levels. For drinking water, a point-of-use reverse osmosis system reduces manganese at the kitchen tap. Retest after treatment to confirm it worked.