Indiana Private Well Water Risk: Arsenic & Nitrate
These figures are USGS statistical estimates for private (domestic) wells in Indiana. They describe the area's modeled risk — not any single well.
Quick answer: Yes — arsenic occurs naturally in Indiana groundwater. USGS modeling estimates about 150,861 Indiana residents rely on private wells with arsenic above the EPA limit of 10 µg/L. The highest modeled exposure is in Kosciusko County (~8,677), Allen County (~7,595), Madison County (~6,936). For nitrate, about 0.1% of Indiana's ~1,410,000 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
0.1%
of the private-well population is modeled above the 10 mg/L nitrate limit
~711
people on wells estimated above the limit
~1,410,000
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
Indiana has one of the higher modeled arsenic exposures in the country — but that number is an area estimate, not your well. 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 Indiana, an estimated ~150,861 people rely on private wells with modeled arsenic above the 10 µg/L EPA limit. The highest modeled exposure is in Kosciusko County (~8,677 people).
Counties with the highest modeled arsenic exposure
| County | Est. well residents over arsenic limit | 90% range |
|---|---|---|
| Kosciusko County | ~8,677 | 6,307–11,702 |
| Allen County | ~7,595 | 5,986–9,573 |
| Madison County | ~6,936 | 5,517–8,622 |
| DeKalb County | ~5,996 | 4,541–7,536 |
| Boone County | ~5,896 | 4,407–7,572 |
| Tippecanoe County | ~5,755 | 4,305–7,520 |
| Jasper County | ~5,552 | 4,328–7,033 |
| St. Joseph County | ~5,356 | 4,096–7,061 |
| Whitley County | ~5,182 | 3,954–6,583 |
| Noble County | ~5,162 | 3,721–6,965 |
| Hancock County | ~5,017 | 3,996–6,279 |
| Hendricks County | ~4,777 | 3,696–6,128 |
| Hamilton County | ~4,107 | 3,367–5,051 |
| Delaware County | ~4,068 | 3,136–5,235 |
| Porter County | ~3,977 | 2,944–5,372 |
| Starke County | ~3,737 | 2,727–5,002 |
| Wells County | ~3,196 | 2,347–4,253 |
| Marshall County | ~3,160 | 2,251–4,360 |
| Lake County | ~3,001 | 2,241–3,983 |
| Adams County | ~2,987 | 2,201–4,015 |
| LaPorte County | ~2,805 | 2,092–3,726 |
| Elkhart County | ~2,680 | 2,088–3,488 |
| Shelby County | ~2,592 | 2,076–3,236 |
| Carroll County | ~2,531 | 1,973–3,190 |
| White County | ~2,288 | 1,771–2,897 |
| Grant County | ~2,231 | 1,574–3,117 |
| Howard County | ~2,158 | 1,657–2,941 |
| Clinton County | ~2,156 | 1,635–2,780 |
| Tipton County | ~1,910 | 1,442–2,520 |
| Jay County | ~1,899 | 1,385–2,543 |
| Huntington County | ~1,869 | 1,407–2,451 |
| Miami County | ~1,722 | 1,379–2,202 |
| Pulaski County | ~1,690 | 1,319–2,146 |
| Marion County | ~1,662 | 1,238–2,236 |
| Steuben County | ~1,509 | 1,194–1,909 |
| LaGrange County | ~1,457 | 1,159–1,832 |
| Henry County | ~1,400 | 1,147–1,706 |
| Montgomery County | ~1,325 | 1,047–1,670 |
| Wabash County | ~1,325 | 1,061–1,654 |
| Johnson County | ~1,224 | 956–1,569 |
| Randolph County | ~938 | 737–1,189 |
| Morgan County | ~851 | 698–1,042 |
| Rush County | ~814 | 661–1,007 |
| Newton County | ~799 | 614–1,090 |
| Bartholomew County | ~724 | 517–1,017 |
| Vigo County | ~647 | 529–791 |
| Fountain County | ~623 | 505–763 |
| Cass County | ~599 | 489–816 |
| Warren County | ~533 | 424–667 |
| Wayne County | ~518 | 427–632 |
| Blackford County | ~512 | 361–715 |
| Decatur County | ~477 | 390–584 |
| Fulton County | ~469 | 366–698 |
| Jackson County | ~348 | 256–476 |
| Clay County | ~321 | 258–398 |
| Putnam County | ~298 | 242–366 |
| Parke County | ~271 | 219–336 |
| Posey County | ~259 | 202–335 |
| Owen County | ~245 | 196–307 |
| Daviess County | ~214 | 174–263 |
| Benton County | ~209 | 162–267 |
| Vanderburgh County | ~151 | 115–199 |
| Jennings County | ~133 | 95–189 |
| Fayette County | ~131 | 109–159 |
| Franklin County | ~118 | 96–146 |
| Vermillion County | ~116 | 95–144 |
| Ripley County | ~100 | 81–123 |
25 additional Indiana counties have lower modeled arsenic exposure (fewer than 100 estimated well residents over the limit). Of these, 10 have measured USGS well samples: Crawford, Gibson, Greene, Harrison, Knox, Lawrence, Martin, Sullivan, Switzerland, Union.
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 50 Indiana 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 |
|---|---|---|---|
| Wayne County | 31% | 2.6 mg/L | 13 wells |
| Shelby County | 17% | 0.1 mg/L | 6 wells |
| Bartholomew County | 14% | 2.7 mg/L | 7 wells |
| Newton County | 11% | 0 mg/L | 18 wells |
| Daviess County | 9% | 0 mg/L | 11 wells |
| Jasper County | 4% | 0 mg/L | 23 wells |
| Lake County | 3% | 0 mg/L | 29 wells |
| Marion County | 2% | 0 mg/L | 41 wells |
Manganese: counties with the most wells > 300 µg/L (EPA health advisory)
| County | Wells over | Median | Sampled |
|---|---|---|---|
| Clay County | 86% | 530 µg/L | 7 wells |
| Daviess County | 80% | 575 µg/L | 10 wells |
| Greene County | 38% | 185 µg/L | 8 wells |
| Lake County | 31% | 118 µg/L | 32 wells |
| Martin County | 20% | 23 µg/L | 59 wells |
| Madison County | 20% | 92 µg/L | 5 wells |
| Jasper County | 18% | 70 µg/L | 22 wells |
| Hamilton County | 17% | 50 µg/L | 6 wells |
| Knox County | 17% | 82 µg/L | 6 wells |
| Marion County | 15% | 110 µg/L | 39 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.
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Indiana well water: FAQ
Is there arsenic in well water in Indiana?
Yes. USGS modeling estimates about 150,861 people in Indiana use private wells with arsenic above 10 µg/L, across 92 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 Indiana counties have the most arsenic in well water?
By modeled number of well residents over the arsenic limit: Kosciusko County (~8,677), Allen County (~7,595), Madison County (~6,936). 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 Indiana?
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 Indiana well water?
USGS models about 0.1% of Indiana's private-well population (~711 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 Indiana?
Acidic well water is uncommon in Indiana, but it does occur. In USGS lab results from 944 wells across 49 Indiana counties, 6% had pH below 6.5. The most acidic sampled counties are Greene County (40% of 10 wells), Porter County (29% of 93 wells), Martin County (15% of 59 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 Indiana well water — what should I do?
In USGS lab results from 364 wells across 20 Indiana counties, 17% were above the EPA's 300 µg/L health advisory for manganese and 56% 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: Clay County (86% of 7 wells), Daviess County (80% of 10 wells), Greene County (38% of 8 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.