Well water in Benton County, Washington
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Testing recommended
tested well samples in Benton County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
2,938 test results across 13 contaminants from at least 439 wells, 1951 to 2016; nitrate has the most at 945. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 27,977 people in Benton County get their drinking water from a private well, per USGS 2015 county water use. That is about 15% of residents.
Separately, the USGS national arsenic model estimates that 19% of the 27,977 people on private wells in Benton County draw water above 10 ug/L (the model's range is 14% to 23%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Benton 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 1951 to 2016 | 945 | 86% | 3.1 | 380 | 10 mg/L EPA limit | |
| Arsenic 1974 to 2016 | 206 | 93% | 4.5 | 18 | 10 ug/L EPA limit | |
| Radium (226 + 228) 1951 to 2016 | 16 | 100% | 1 | 7.7 | 5 pCi/L EPA limit | |
| Fluoride 1951 to 2016 | 405 | 100% | 0.4 | 38 | 4 mg/L EPA limit | |
| Lead 1970 to 2016 | 53 | 38% | 0 | 0.4 | 15 ug/L EPA limit | |
| Copper 1970 to 2016 | 46 | 46% | 0 | 0.05 | 1.3 mg/L EPA limit | |
| Chloride 1951 to 2016 | no limit | 494 | 100% | 12 | 170 | 250 mg/L nuisance level |
| Sodium 1951 to 2016 | no limit | 407 | 100% | 26 | 700 | 20 mg/L health guideline |
| Iron 1951 to 2016 | no limit | 199 | 83% | 30 | 3,900 | 300 ug/L nuisance level |
| Manganese 1969 to 2016 | no limit | 164 | 63% | 0 | 3,700 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: E. coli (1), Uranium (1), 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
The contaminants most often above their limit here are nitrate (15% of 945 samples), arsenic (8% of 206 samples), and radium (226 + 228) (6% of 16 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 Benton County
- 1Nitrate15% of 945 local samples were above the limit.
- 2Arsenic8% of 206 local samples were above the limit.
- 3Radium (226 + 228)6% of 16 local samples were above the limit.
- 4Fluoride3% of 405 local samples were above the limit.
- 5Coliform bacteriaRecommended for every private well, every year.
- 6RadonMedian local reading is 430 pCi/L.
- 7ChlorideDetected in 100% of local samples.
- 8Volatile organic compounds (VOCs)14 reported spills and releases on record locally.
Test your Benton County well for nitrate, arsenic and radium (226 + 228)
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 Washington: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Benton County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Benton County
4,457 domestic wells in Benton County are on record with the state since 1993. the typical well is 162 feet deep (one in ten goes past 475 feet).
In a typical Benton County well, the median yield is 32.5 gallons per minute, 5% 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 Ecology well report search and choose Water Well.
- It lists depth, casing, static water level, the yield test and the driller.
Washington has required well reports since 1971; reports are located only to the quarter-quarter section, so check the address on the scan.
The rock under Benton County
Columbia Plateau basin-fill aquifers
Unconsolidated sand and gravel. Wells in sand and gravel are usually shallow and productive, and they recharge quickly from the surface. That makes them the most exposed to nitrate, bacteria and anything spilled nearby, and the least likely to carry arsenic or radon from the rock.
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 Washington
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.
- Drinking Water, Washington State Department of Health
- Environmental lab accreditation, Washington State Department of Ecology
Contamination sources on record in Benton County
Washington Ecology facility interactions records 14 reported spills and releases in Benton County, among 927 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.
- 14
- reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
- 873
- other remediation projects
- 40
- other solid waste facilities
Treatment that fits the local profile
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Radium (226 + 228)
Water softener (cation exchange); Point-of-use reverse osmosis
Fluoride
Point-of-use reverse osmosis; Activated alumina; 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 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 arsenic
Whole-house arsenic and uranium filter
whole-house, at the point of entry, about $2,500
Adsorptive iron-based media; sized to your well yield.
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
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Common questions
How deep are wells in Benton County?
The typical domestic well in Benton County is 162 feet deep, based on 4,457 wells reported to the state since 1993. One in ten is deeper than 475 feet.
Is there arsenic in well water in Benton County?
Arsenic was detected in 93% of 206 public well samples in Benton County, and 8% 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 Benton 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 Benton 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 Washington dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 2,938 samples in Benton 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 27,977 people on private wells in Benton 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.
- Washington Ecology well construction reports: 4,462 well records in Benton County, 4,457 domestic. Well construction reports filed with the Washington State Department of Ecology, water wells only, located at the quarter-quarter section. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 17, 2026.
- Washington Ecology facility interactions: 927 regulated sites located in Benton County. Toxics cleanup sites, spills and solid waste facilities from the Washington State Department of Ecology Facility/Site register. Retrieved September 17, 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.