Well water in Washington County, Missouri
In Washington County, 4% of 84 private wells tested between 2010 and 2023 had lead above the EPA limit (15 ug/L), according to Missouri DHSS.
228 private wells tested 2010 to 2023 in state summaries; 70 test results across 11 contaminants from at least 11 wells, 1940 to 1998; nitrate has the most at 17. 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 17,808 people in Washington County get their drinking water from a private well, per USGS 2015 county water use. That is about 72% of residents.
Separately, the USGS national arsenic model estimates that <1% of the 17,808 people on private wells in Washington County draw water above 10 ug/L (the model's range is <1% to 1%), 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 Washington 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 1949 to 1998 | 17 | 76% | 0 | 2.61 | 10 mg/L EPA limit | |
| Chloride 1940 to 1993 | no limit | 11 | 100% | 6.2 | 11 | 250 mg/L nuisance level |
| Iron 1940 to 1993 | no limit | 11 | 100% | 80 | 740 | 300 ug/L nuisance level |
| Manganese 1940 to 1993 | no limit | 10 | 100% | 0 | 50 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: Fluoride (9), Copper (1), Uranium (1), Lead (1), Arsenic (1), Sodium (7), Radon (1).
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 Washington County who sent a sample to the state lab, the health-based limits most often exceeded were lead (4% of 84 wells) and nitrate (<1% of 228 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.
Iron exceeds the state's advisory level in a sizable share of wells; this is mostly a taste, staining or diet issue rather than a toxicity one.
What to test for in Washington County
- 1Lead4% of 84 local wells tested were above the EPA limit.
- 2Nitrate<1% of 228 local wells tested were above the EPA limit.
- 3Coliform bacteriaRecommended for every private well, every year.
- 4RadonMedian local reading is 280 pCi/L.
- 5Iron12% of 34 local wells tested were above the EPA secondary standard.
- 6Chloride5% of 20 local wells tested were above the EPA secondary standard.
- 7FluorideDetected in 100% of local samples.
- 8CopperDetected in 100% of local samples.
- 9Volatile organic compounds (VOCs)6 hazardous waste sites on record locally.
- 10Metals panel6 hazardous waste sites on record locally.
Test your Washington County well for lead, nitrate 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 Washington County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Washington County
3,127 domestic wells in Washington County are on record with the state since 1987. the typical well is 206 feet deep (one in ten goes past 390 feet).
In a typical Washington County well, the median yield is 20 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 Washington County
Ozark Plateaus aquifer system
Carbonate-rock. Limestone and dolomite move water through cracks and solution channels, sometimes very fast. Bacteria and nitrate can travel from the surface to a well in days, so annual bacteria testing matters more here than most places; hardness is a given.
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 Washington County
Missouri DNR records 6 hazardous waste sites in Washington County, among 22 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.
- 6
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 13
- registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
- 2
- lined landfills and transfer facilities
- 1
- other solid waste facility
Treatment that fits the local profile
Iron
Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Chloride
Point-of-use reverse osmosis; Distillation
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 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.
For chloride
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
Free, no obligation
Get on the list for a free in-home water test in Washington County
No water treatment company serves Washington 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 Washington County, and you get an email naming it first.
Common questions
How deep are wells in Washington County?
The typical domestic well in Washington County is 206 feet deep, based on 3,127 wells reported to the state since 1987. One in ten is deeper than 390 feet.
How often should I test a private well in Washington 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 Washington 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: 70 samples in Washington 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 Washington County, up to 228 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 17,808 people on private wells in Washington 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: 3,408 well records in Washington County, 3,127 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: 22 regulated sites located in Washington 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.