Private wells
Missouri well water: who's on a well and what to test for
People on private wells
1,232,000
Homes on wells
20.2%
Est. above arsenic limit
10,200
Every Missouri county
Sorted by people on private wells. Arsenic and nitrate are modeled for typical wells in the county, not measured at yours; depth is the median of domestic well records.
| Jefferson County | 72,200 | 32% | 2.4% | 0.1 | 330 ft |
| Franklin County | 48,600 | 46% | 1.9% | 0.1 | 306 ft |
| Greene County | 43,100 | 13% | 1.5% | 0.2 | 425 ft |
| Newton County | 31,100 | 51% | 1.2% | 0.1 | 405 ft |
| St. Charles County | 27,200 | 7% | 5.5% | 0.0 | 400 ft |
| St. Louis County | 26,500 | 2% | 2.3% | 0.1 | 400 ft |
| Camden County | 26,500 | 61% | 1.3% | 0.1 | 280 ft |
| Christian County | 26,100 | 29% | 1.3% | 0.2 | 450 ft |
| Jasper County | 24,600 | 19% | 1.4% | 0.2 | 300 ft |
| Webster County | 23,200 | 58% | 1.2% | 0.2 | 335 ft |
| Lincoln County | 23,200 | 39% | 2.5% | 0.0 | 405 ft |
| Cole County | 22,300 | 26% | 1.8% | 0.2 | 286 ft |
| Jackson County | 21,200 | 3% | 2.8% | 0.4 | 160 ft |
| St. Francois County | 20,600 | 33% | 2.2% | 0.2 | 270 ft |
| Boone County | 20,300 | 10% | 1.6% | 0.0 | 426 ft |
| Howell County | 20,200 | 49% | 1.1% | 0.3 | 326 ft |
| Phelps County | 18,500 | 41% | 1.1% | 0.1 | 275 ft |
| Taney County | 18,000 | 28% | 1.3% | 0.0 | 410 ft |
| Barry County | 17,600 | 53% | 1.2% | 0.2 | 400 ft |
| Stone County | 17,400 | 53% | 1.2% | 0.1 | 410 ft |
| Polk County | 17,200 | 54% | 1.3% | 0.2 | 315 ft |
| Washington County | 16,900 | 72% | 1.5% | 0.1 | 210 ft |
| Lawrence County | 16,300 | 40% | 1.4% | 0.2 | 434 ft |
| Johnson County | 16,000 | 29% | 2.1% | 0.1 | 430 ft |
| Miller County | 16,000 | 61% | 1.5% | 0.2 | 260 ft |
| Callaway County | 15,500 | 37% | 1.8% | 0.0 | 407 ft |
| Morgan County | 15,500 | 77% | 1.5% | 0.1 | 250 ft |
| Butler County | 15,300 | 36% | 2.6% | 0.1 | 230 ft |
| Cape Girardeau County | 14,900 | 17% | 2.4% | 0.2 | 300 ft |
| Texas County | 14,600 | 62% | 1.0% | 0.2 | 317 ft |
| Pettis County | 14,600 | 30% | 2.7% | 0.1 | 310 ft |
| Warren County | 14,100 | 40% | 1.9% | 0.0 | 426 ft |
| Laclede County | 13,700 | 38% | 1.2% | 0.1 | 327 ft |
| Crawford County | 13,600 | 60% | 1.2% | 0.1 | 266 ft |
| McDonald County | 13,200 | 58% | 1.1% | 0.1 | 415 ft |
| Dallas County | 13,200 | 76% | 1.3% | 0.2 | 300 ft |
| Cass County | 12,900 | 12% | 1.3% | 0.1 | 288 ft |
| Pulaski County | 12,600 | 28% | 1.3% | 0.1 | 315 ft |
| Benton County | 12,300 | 63% | 1.4% | 0.1 | 260 ft |
| Wright County | 11,500 | 60% | 1.2% | 0.2 | 335 ft |
| Scott County | 10,200 | 25% | 13.8% | 0.4 | 240 ft |
| Stoddard County | 9,500 | 32% | 6.0% | 0.1 | 157 ft |
| Ste. Genevieve County | 9,500 | 52% | 3.7% | 0.1 | 265 ft |
| Dent County | 8,800 | 60% | 1.0% | 0.1 | 295 ft |
| Douglas County | 8,700 | 74% | 1.2% | 0.2 | 335 ft |
| Lafayette County | 8,700 | 26% | 2.4% | 0.2 | 365 ft |
| Osage County | 8,700 | 65% | 1.7% | 0.1 | 326 ft |
| Bollinger County | 8,500 | 80% | 1.6% | 0.1 | 276 ft |
| Ray County | 7,900 | 34% | 2.6% | 0.7 | 68 ft |
| Gasconade County | 7,800 | 52% | 1.3% | 0.1 | 306 ft |
| Perry County | 7,500 | 41% | 1.9% | 0.2 | 327 ft |
| Henry County | 7,300 | 33% | 1.8% | 0.1 | 360 ft |
| Wayne County | 7,300 | 68% | 1.3% | 0.1 | 240 ft |
| Ozark County | 7,300 | 85% | 1.1% | 0.1 | 350 ft |
| Platte County | 7,200 | 6% | 3.1% | 0.5 | 87 ft |
| Clay County | 7,200 | 3% | 2.7% | 0.2 | 100 ft |
| Clinton County | 7,100 | 34% | 2.0% | 0.8 | 60 ft |
| Cedar County | 7,100 | 48% | 2.5% | 0.1 | 375 ft |
| Vernon County | 7,100 | 34% | 2.4% | 0.1 | 385 ft |
| Ripley County | 6,800 | 64% | 1.3% | 0.3 | 240 ft |
| Audrain County | 6,800 | 25% | 2.8% | 0.0 | 360 ft |
| Buchanan County | 6,600 | 7% | 2.7% | 1.5 | 50 ft |
| Moniteau County | 6,600 | 41% | 1.6% | 0.3 | 290 ft |
| Hickory County | 6,500 | 78% | 1.2% | 0.1 | 335 ft |
| Madison County | 6,400 | 53% | 1.5% | 0.1 | 273 ft |
| Maries County | 6,400 | 75% | 1.3% | 0.1 | 290 ft |
| Pike County | 6,400 | 37% | 5.5% | 0.1 | 404 ft |
| Adair County | 6,300 | 26% | 1.7% | 0.8 | n/a |
| Ralls County | 6,200 | 58% | 3.1% | 0.1 | 240 ft |
| Bates County | 6,200 | 38% | 1.4% | 0.3 | 305 ft |
| St. Clair County | 6,100 | 64% | 2.9% | 0.1 | 310 ft |
| Macon County | 6,100 | 39% | 1.9% | 1.4 | n/a |
| Nodaway County | 6,000 | 25% | 2.6% | 2.9 | 48 ft |
| Cooper County | 5,800 | 35% | 3.0% | 0.2 | 350 ft |
| Andrew County | 5,800 | 31% | 4.8% | 2.3 | 47 ft |
| Randolph County | 5,800 | 23% | 1.5% | 0.2 | 425 ft |
| Lewis County | 5,700 | 60% | 2.2% | 0.1 | 179 ft |
| Oregon County | 5,600 | 64% | 1.0% | 0.3 | 320 ft |
| Iron County | 5,500 | 58% | 1.4% | 0.1 | 240 ft |
| Marion County | 5,300 | 18% | 3.5% | 0.2 | 145 ft |
| Montgomery County | 5,100 | 48% | 3.7% | 0.0 | 407 ft |
| Shannon County | 5,000 | 69% | 1.1% | 0.1 | 360 ft |
| Saline County | 4,700 | 22% | 5.0% | 0.1 | 370 ft |
| Dunklin County | 4,600 | 16% | 8.3% | 0.4 | 100 ft |
| Reynolds County | 4,500 | 76% | 1.1% | 0.1 | 290 ft |
| Dade County | 4,400 | 57% | 2.1% | 0.1 | 400 ft |
| Barton County | 4,200 | 34% | 2.9% | 0.0 | n/a |
| Monroe County | 4,100 | 50% | 3.3% | 0.1 | 270 ft |
| Howard County | 4,000 | 41% | 2.1% | 0.1 | 350 ft |
| Daviess County | 3,700 | 39% | 2.8% | 0.9 | 60 ft |
| Caldwell County | 3,600 | 38% | 2.0% | 1.2 | 50 ft |
| Clark County | 3,600 | 53% | 2.2% | 0.3 | 185 ft |
| New Madrid County | 3,600 | 20% | 7.4% | 0.3 | 80 ft |
| Carter County | 3,500 | 65% | 1.4% | 0.2 | 230 ft |
| Livingston County | 3,400 | 24% | 3.6% | 0.3 | 110 ft |
| Knox County | 3,400 | 87% | 1.5% | 0.0 | 265 ft |
| Shelby County | 3,300 | 54% | 2.6% | 0.2 | n/a |
| Pemiscot County | 3,200 | 19% | 6.8% | 0.1 | n/a |
| Grundy County | 3,200 | 28% | 4.3% | 0.2 | 135 ft |
| Chariton County | 3,100 | 38% | 3.7% | 0.5 | 80 ft |
| Harrison County | 3,100 | 36% | 1.6% | 1.6 | 58 ft |
| DeKalb County | 3,000 | 31% | 2.4% | 1.4 | 53 ft |
| Mississippi County | 3,000 | 26% | 17.6% | 0.5 | n/a |
| Carroll County | 2,900 | 34% | 3.1% | 0.5 | 60 ft |
| Linn County | 2,700 | 22% | 2.5% | 0.7 | 120 ft |
| Scotland County | 2,500 | 47% | 2.1% | 1.0 | n/a |
| Schuyler County | 2,500 | 56% | 2.2% | 1.3 | n/a |
| Putnam County | 2,400 | 50% | 1.9% | 1.1 | n/a |
| Sullivan County | 2,300 | 39% | 2.3% | 1.3 | n/a |
| Gentry County | 2,100 | 32% | 2.7% | 1.8 | 42 ft |
| Mercer County | 2,000 | 55% | 2.3% | 1.0 | n/a |
| Atchison County | 1,800 | 34% | 8.1% | 1.8 | 64 ft |
| Holt County | 1,700 | 42% | 9.0% | 0.9 | 72 ft |
| Worth County | 1,300 | 66% | 3.1% | 1.8 | 42 ft |
| St. Louis city | 20 | 0% | 3.2% | 0.6 | n/a |
Shading: red is among the highest counties nationally, amber the middle, green the lower range. Click a column to sort.
Most well users above the arsenic limit
- Greene County: about 620 people
- Lincoln County: about 550 people
- Pettis County: about 490 people
- Franklin County: about 470 people
- Camden County: about 430 people
Test first, then treat what the test finds
We may earn a commission from links below, at no cost to you. Picks follow the testing order, not who pays. How we make money.
1. Certified lab well test
Start here, every year
A mail-in kit analyzed by a certified lab measures bacteria, nitrate, arsenic, metals and more. Test strips cannot measure arsenic or uranium reliably.
Mail-in certified lab well water test
Mid-range2. Sediment pre-filter
Sand, silt or cloudy water
A 5-micron cartridge after the pressure tank catches sand, silt and rust before they reach fixtures or other filters. Cartridges are cheap and swap every few months.
5-micron whole-house sediment filter
Budget3. Iron and sulfur filter
Orange stains or rotten-egg smell
Air-injection or oxidizing-media filters remove orange staining and rotten-egg smell. Size one from a lab result for iron, manganese and hydrogen sulfide.
Air-injection iron and sulfur filter
Premium4. UV disinfection system
Coliform bacteria in a test
Inactivates bacteria and viruses; usually for private wells or after boil notices.
12 GPM whole-house UV purifier
Premium5. Under-sink reverse osmosis
Arsenic, nitrate or uranium in a test
The most thorough option for drinking water: PFAS, lead, nitrate, arsenic and more. Look for NSF/ANSI 58.
Waterdrop G3P600 tankless RO
Price at Waterdrop, checked Oct 5, 2026or compare on Amazon
iSpring RCC7AK reverse osmosis
Mid-range6. Whole-house well filter
Several problems at once
Multi-stage sediment and carbon for every tap. Add UV if bacteria shows up, and choose stages from your lab results, not a guess.
Waterdrop WHF21 2-stage whole-house filter
Mid-rangeQuestions
Which Missouri counties rely most on wells?+
By share of homes: Knox County (87%), Ozark County (85%), Bollinger County (80%), Hickory County (78%), Morgan County (77%). By number of people: Jefferson County (72,200), Franklin County (48,600), Greene County (43,100).
Is arsenic a problem in Missouri wells?+
USGS estimates about 10,200 Missouri well users have water above the 10 microgram per liter arsenic limit that applies to public systems, the largest numbers in Greene County, Lincoln County, Pettis County. Arsenic has no taste or smell, so only a lab test finds it.
Do I have to test my well when I sell a house in Missouri?+
We could not confirm a statewide rule for Missouri. Check with your county health department. Buyers can still make a lab test a condition of the offer.
How often should I test my well?+
No federal law covers private wells. EPA's drinking water limits apply to public water systems, so testing and treating a private well is up to the owner. EPA and CDC recommend testing at least once a year for coliform bacteria, nitrate, pH and total dissolved solids, and testing for arsenic, uranium, radon and other local concerns based on where you live.
Well-user counts, arsenic and nitrate figures are each a modeled estimate built from national datasets, not a count of tested wells, and well depths summarize drilling records rather than every well. Your own well can be very different from the county average, which is why the only answer for your home is a lab test. Sources: EPA Office of Research and Development, Water Source 2020 (private well estimates by census block); CDC Environmental Public Health Tracking, Well Water Index (from USGS nitrate and arsenic models); USGS, county-level domestic well population with arsenic above 10 micrograms per liter (Ayotte and others, 2017); USGS Synthesized Domestic Well Database for the Conterminous United States (SynDWell-US), McCarthy and others, 2025 (depth, where a county has 30+ usable records).