Well water in Dewey County, South Dakota
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Testing recommended
tested well samples in Dewey County exceeded the EPA limit for fluoride (4 mg/L), based on public data from USGS Water Quality Portal.
568 test results across 9 contaminants from at least 81 wells, 1936 to 1995; chloride has the most at 113. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 1,407 people in Dewey County get their drinking water from a private well, per USGS 2015 county water use. That is about 25% of residents.
Separately, the USGS national arsenic model estimates that <1% of the 1,407 people on private wells in Dewey County draw water above 10 ug/L, from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Dewey 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 |
|---|---|---|---|---|---|---|
| Fluoride 1937 to 1994 | 67 | 99% | 0.4 | 4.8 | 4 mg/L EPA limit | |
| Nitrate 1953 to 1994 | 93 | 66% | 0.1 | 7,000 | 10 mg/L EPA limit | |
| Lead 1972 to 1994 | 15 | 73% | 0 | 2 | 15 ug/L EPA limit | |
| Arsenic 1972 to 1994 | 12 | 58% | 0 | 4 | 10 ug/L EPA limit | |
| Copper 1972 to 1994 | 10 | 90% | 0 | 0.011 | 1.3 mg/L EPA limit | |
| Chloride 1936 to 1995 | no limit | 113 | 100% | 44 | 8,870 | 250 mg/L nuisance level |
| Sodium 1951 to 1994 | no limit | 90 | 100% | 297 | 51,200 | 20 mg/L health guideline |
| Iron 1938 to 1994 | no limit | 89 | 93% | 400 | 52,000 | 300 ug/L nuisance level |
| Manganese 1938 to 1994 | no limit | 79 | 76% | 50 | 10,000 | 300 ug/L health guideline |
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
The contaminants most often above their limit here are fluoride (9% of 67 samples) and nitrate (8% of 93 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.
Chloride, Iron, and Manganese are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Dewey County
- 1Fluoride9% of 67 local samples were above the limit.
- 2Nitrate8% of 93 local samples were above the limit.
- 3Coliform bacteriaRecommended for every private well, every year.
- 4ChlorideDetected in 100% of local samples.
- 5IronDetected in 93% of local samples.
- 6CopperDetected in 90% of local samples.
- 7ManganeseDetected in 76% of local samples.
- 8Volatile organic compounds (VOCs)82 reported spills and releases on record locally.
Test your Dewey County well for fluoride, 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 South Dakota: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Dewey County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Dewey County
379 domestic wells in Dewey County are on record with the state since 1970. the typical well is 91 feet deep (one in ten goes past 2,364 feet).
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 DANR well completion reports and choose Water Well.
- It lists depth, aquifer, static water level and the driller.
South Dakota has required reports since 1986.
The rock under Dewey 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 South Dakota
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.
- Test a Private Well, South Dakota Department of Health
- Drinking Water Program - Laboratory Certification, South Dakota DANR
Contamination sources on record in Dewey County
South Dakota DANR tank facilities and spills records 82 reported spills and releases in Dewey County, among 118 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.
- 82
- reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
- 20
- registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
- 16
- other solid waste facilities
Treatment that fits the local profile
Fluoride
Point-of-use reverse osmosis; Activated alumina; Distillation
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 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 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 Dewey County
No water treatment company serves Dewey 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 Dewey County, and you get an email naming it first.
Common questions
How deep are wells in Dewey County?
The typical domestic well in Dewey County is 91 feet deep, based on 379 wells reported to the state since 1970. One in ten is deeper than 2,364 feet.
Is there arsenic in well water in Dewey County?
Arsenic was detected in 58% of 12 public well samples in Dewey County, and 0% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How often should I test a private well in Dewey 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 Dewey 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 South Dakota dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 568 samples in Dewey 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.
- USGS national arsenic model (Ayotte 2017): estimated share of 1,407 people on private wells in Dewey 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.
- South Dakota DANR well completion reports: 571 well records in Dewey County, 379 domestic. Well completion reports filed with the South Dakota Department of Agriculture and Natural Resources. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 18, 2026.
- South Dakota DANR tank facilities and spills: 118 regulated sites located in Dewey County. Regulated tank facilities and spill reports from the South Dakota Department of Agriculture and Natural Resources. Retrieved September 18, 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.