Well water in St. Louis County, Missouri
In St. Louis County, none of 39 private wells tested between 2010 and 2023 had lead above the EPA limit (15 ug/L), according to Missouri DHSS.
The strongest signal is coliform bacteria: Recommended for every private well, every year, too few samples to carry the headline but first on the test list below.
39 private wells tested 2010 to 2023 in state summaries; 26 test results across 6 contaminants from at least 3 wells, 1936 to 1942; chloride has the most at 6. 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.
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.
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 St. Louis County who sent a sample to the state lab, no health-based limit was exceeded often enough to publish a share. That is good news, but a single well can still be the exception.
What to test for in St. Louis County
- 1Coliform bacteriaRecommended for every private well, every year.
- 2NitrateRecommended for every private well, especially near farms or septic systems.
- 3FluorideDetected in 100% of local samples.
- 4ChlorideDetected in 100% of local samples.
- 5IronDetected in 100% of local samples.
- 6ManganeseDetected in 100% of local samples.
Test your St. Louis County well for coliform bacteria, nitrate and fluoride
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 St. Louis County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under St. Louis 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 St. Louis County
Missouri DNR records 7 regulated sites in St. Louis County, among 7 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.
- 2
- lined landfills and transfer facilities
- 5
- other solid waste facilities
Treatment that fits the local profile
Fluoride
Point-of-use reverse osmosis; Activated alumina; Distillation
Chloride
Point-of-use reverse osmosis; Distillation
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 fluoride
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For fluoride
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 manganese
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 St. Louis County
No water treatment company serves St. Louis 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 St. Louis County, and you get an email naming it first.
Common questions
How often should I test a private well in St. Louis 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 St. Louis 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: 26 samples in St. Louis 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 4 contaminants in St. Louis County, up to 39 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.
- Missouri DNR regulated sites: 7 regulated sites located in St. Louis 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.