Well water in Johnson County, Missouri
In Johnson County, 5% of 65 tested well samples exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
58 private wells tested 2010 to 2023 in state summaries; 305 test results across 9 contaminants from at least 44 wells, 1934 to 1998; nitrate has the most at 65. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
Missouri does not require private well testing, so these are samples homeowners chose to send to the state lab, often after a problem; shares above the limit run higher than a random survey would find.
An estimated 3,851 people in Johnson County get their drinking water from a private well, per USGS 2015 county water use. That is about 7% of residents.
Separately, the USGS national arsenic model estimates that <1% of the 3,851 people on private wells in Johnson County draw water above 10 ug/L, from geology and well depth rather than local tests.
What homeowner tests found
Missouri DHSS private well sampling summaries: private wells tested and reported to the state, 2010 to 2023. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA.
What individual samples found
Each row summarizes every public sample for that contaminant inside Johnson County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Above limit | Samples | Detected | Median | Highest | Limit |
|---|---|---|---|---|---|---|
| Nitrate 1934 to 1998 | 65 | 75% | 0 | 62 | 10 mg/L EPA limit | |
| Fluoride 1935 to 1971 | 32 | 100% | 0.8 | 3.7 | 4 mg/L EPA limit | |
| Chloride 1934 to 1971 | no limit | 62 | 100% | 94.8 | 3,800 | 250 mg/L nuisance level |
| Sodium 1934 to 1971 | no limit | 61 | 100% | 225 | 2,620 | 20 mg/L health guideline |
| Iron 1934 to 1971 | no limit | 52 | 100% | 245 | 6,400 | 300 ug/L nuisance level |
| Manganese 1935 to 1971 | no limit | 26 | 92% | 5 | 350 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: Copper (3), Arsenic (2), Lead (2).
Closer than the county
See the sampled wells near your address
The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.
Check my addressWhat this means
Among homeowners in Johnson County who sent a sample to the state lab, the health-based limits most often exceeded were lead (3% of 58 wells). These are ordinary wells tested by their owners, so the shares are the best available picture of a typical well here, with one caveat: people test more often when they suspect a problem.
What to test for in Johnson County
- 1Nitrate5% of 65 local samples were above the limit.
- 2Lead3% of 58 local wells tested were above the EPA limit.
- 3Coliform bacteriaRecommended for every private well, every year.
- 4FluorideDetected in 100% of local samples.
- 5ChlorideDetected in 100% of local samples.
- 6IronDetected in 100% of local samples.
- 7ManganeseDetected in 92% of local samples.
- 8CopperDetected in 67% of local samples.
- 9Volatile organic compounds (VOCs)1 leaking underground storage tank site on record locally.
- 10Metals panel3 hazardous waste sites on record locally.
Test your Johnson County well for nitrate, lead and coliform bacteria
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
Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.
Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.
Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.
Where to get a well tested in Missouri: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Johnson County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Johnson County
934 domestic wells in Johnson County are on record with the state since 1987. the typical well is 475 feet deep (one in ten goes past 727 feet).
In a typical Johnson County well, the median yield is 30 gallons per minute, <1% of wells yield under 3 gallons per minute and usually need a storage tank.
Find your own well's report
The state keeps the driller's report for most wells drilled since 1984. It tells you how deep your well is, where bedrock starts, and how much water it makes, which decides what treatment can work.
- Open Missouri DNR WIMS and choose Water Well.
- The certification record lists total depth, casing length, static water level, yield and the driller.
Missouri has required certification of new private wells since 1987, so a well drilled before then usually has no record.
The rock under Johnson County
Not a principal aquifer
The USGS map places this area outside any principal aquifer, which usually means wells here draw from fractured bedrock or thin local deposits rather than a large regional aquifer. Bedrock wells of that kind are where arsenic, radon and uranium turn up, and yields vary from well to well.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in Missouri
Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.
- Private Drinking Water, Missouri DHSS
- Certified Laboratories, Missouri DNR
Contamination sources on record in Johnson County
Missouri DNR records 1 leaking underground storage tank site and 3 hazardous waste sites in Johnson County, among 17 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 1
- leaking underground storage tank siteGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 3
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 9
- registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
- 4
- lined landfills and transfer facilities
Treatment that fits the local profile
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Chloride
Point-of-use reverse osmosis; Distillation
Iron
Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Manganese
Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
Systems we would look at first
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.
For iron
Iron and manganese oxidizing filter
whole-house, at the point of entry, about $1,800
Air-injection or greensand media; fixes staining at the source.
Free, no obligation
Get on the list for a free in-home water test in Johnson County
No water treatment company serves Johnson County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Johnson County, and you get an email naming it first.
Common questions
How deep are wells in Johnson County?
The typical domestic well in Johnson County is 475 feet deep, based on 934 wells reported to the state since 1987. One in ten is deeper than 727 feet.
How often should I test a private well in Johnson County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Counties near Johnson County
Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.
Want the numbers themselves? Download the Missouri dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 305 samples in Johnson County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- Missouri DHSS private well sampling summaries: summaries for 7 contaminants in Johnson County, up to 58 wells each. County summaries of private well samples analyzed by the Missouri State Public Health Laboratory, 2010 to 2023, published by the Missouri Department of Health and Senior Services. Counts are samples, not distinct wells. Shares are against the EPA maximum contaminant level, or the EPA secondary standard for chloride and iron. Counties with fewer than 20 samples are flagged unreliable by DHSS and are kept here with their counts so the threshold rule can judge them. Barium, sulfate and zinc layers exist but have no contaminant page yet. Retrieved September 15, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 3,851 people on private wells in Johnson County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
- Missouri DNR certified well records: 2,129 well records in Johnson County, 934 domestic. Well certification records from the Missouri Department of Natural Resources Wellhead Information Management System (WIMS), published through MSDIS. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 15, 2026.
- Missouri DNR regulated sites: 17 regulated sites located in Johnson County. Permitted solid waste facilities, and leaking tank, underground tank and hazardous waste sites from the historical CARES potential contaminant site inventory, Missouri Department of Natural Resources. Retrieved September 15, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.