Well water in Washington County, Rhode Island
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Testing strongly recommended
tested well samples in Washington County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
3,012 test results across 15 contaminants from at least 302 wells, 1954 to 2025; nitrate has the most at 1,726. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 36,690 people in Washington County get their drinking water from a private well, per USGS 2015 county water use. That is about 29% of residents.
Separately, the USGS national arsenic model estimates that 1% of the 36,690 people on private wells in Washington County draw water above 10 ug/L (the model's range is 1% to 2%), from geology and well depth rather than local tests.
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 1955 to 2025 | 1,726 | 94% | 6.59 | 3,280 | 10 mg/L EPA limit | |
| Radium (226 + 228) 1981 to 2019 | 36 | 67% | 0.04 | 14 | 5 pCi/L EPA limit | |
| E. coli 2011 to 2025 | 22 | 9% | 0 | 21,900 | 0 MPN/100mL EPA limit | |
| Fluoride 1955 to 2025 | 91 | 57% | 0.1 | 84 | 4 mg/L EPA limit | |
| Copper 1955 to 2019 | 45 | 89% | 0.004 | 0.13 | 1.3 mg/L EPA limit | |
| Lead 1973 to 2019 | 44 | 64% | 0 | 10 | 15 ug/L EPA limit | |
| Arsenic 1982 to 2019 | 15 | 47% | 0 | 1 | 10 ug/L EPA limit | |
| Uranium 1955 to 2019 | 12 | 100% | 0.673 | 4.36 | 30 ug/L EPA limit | |
| Chloride 1954 to 2025 | no limit | 418 | 100% | 19.3 | 1,950 | 250 mg/L nuisance level |
| Iron 1954 to 2019 | no limit | 266 | 89% | 60 | 210,000 | 300 ug/L nuisance level |
| Manganese 1955 to 2019 | no limit | 227 | 89% | 40 | 3,700 | 300 ug/L health guideline |
| Sodium 1955 to 2019 | no limit | 102 | 100% | 10 | 170 | 20 mg/L health guideline |
Sampled fewer than 10 times, too few to summarize: PFOA (2), PFOS (2), Radon (4).
Over time
Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.
| Contaminant | before 2000 | 2000s | 2010s | 2020s |
|---|---|---|---|---|
| Nitrate | 46%1,606 samples | 0%14 samples | n/a | 16%98 samples |
| Fluoride | 3%62 samples | n/a | n/a | 0%18 samples |
Nitrate above the limit in Washington County fell from 46% of 1606 samples before 2000 to 16% of 98 in the 2020s.
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 (44% of 1,726 samples), radium (226 + 228) (22% of 36 samples), and e. coli (9% of 22 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.
The median radon reading (2,505 pCi/L) is above the 2,000 pCi/L level at which treatment is recommended. Radon in water raises indoor air radon when it is used for showers and laundry.
What to test for in Washington County
- 1Nitrate44% of 1,726 local samples were above the limit.
- 2Radium (226 + 228)22% of 36 local samples were above the limit.
- 3E. coli9% of 22 local samples were above the limit.
- 4Fluoride2% of 91 local samples were above the limit.
- 5RadonMedian local reading is 2,505 pCi/L.
- 6PFOAAbove the limit in 2 of 2 local samples; too few to quote a rate.
- 7PFOSAbove the limit in 2 of 2 local samples; too few to quote a rate.
- 8Volatile organic compounds (VOCs)226 leaking underground storage tank sites on record locally.
- 9PFAS13 unlined landfills on record locally.
- 10Metals panel199 hazardous waste sites on record locally.
Test your Washington County well for nitrate, radium (226 + 228) and E. coli
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 Rhode Island: 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.
The rock under Washington 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 Rhode Island
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 Wells, RIDOH
- Certified Drinking Water Testing Labs, RIDOH
Contamination sources on record in Washington County
RIDEM records 226 leaking underground storage tank sites, 13 unlined landfills, and 199 hazardous waste sites in Washington County, among 568 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.
- 226
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 13
- unlined landfillsOlder unlined landfills are a leading source of PFAS, VOCs and metals in nearby wells.
- 199
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 119
- other remediation projects
- 11
- other solid waste facilities
Treatment that fits the local profile
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Radium (226 + 228)
Water softener (cation exchange); Point-of-use reverse osmosis
E. coli
Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system
Fluoride
Point-of-use reverse osmosis; Activated alumina; Distillation
Radon
Aeration (bubble-up or diffused) whole-house; Granular activated carbon whole-house (lower levels only)
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 E. coli
UV disinfection system
whole-house, at the point of entry, about $900
Fix the well cap and casing first; UV keeps bacteria from returning.
For E. coli
Aquasana Rhino Well Water with UV
whole-house, at the point of entry, about $2,871
Whole-house system built for wells: sediment pre-filter, KDF and carbon, and a UV lamp rated to kill 99.99% of bacteria and viruses. It does not remove arsenic, nitrate, uranium or radon.
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
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Common questions
Is there arsenic in well water in Washington County?
Arsenic was detected in 47% of 15 public well samples in Washington 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 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.
Towns in Washington County
- Charlestown66% nitrate
- New Shoreham2% nitrate
- North Kingstown19% nitrate
- Richmond43% nitrate
- South Kingstown2% nitrate
4 towns have fewer than 30 public samples and are included in the Washington County totals above rather than shown separately: Exeter, Hopkinton, Narragansett, Westerly.
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 Rhode Island dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 3,012 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.
- USGS national arsenic model (Ayotte 2017): estimated share of 36,690 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.
- RIDEM regulated facilities: 568 regulated sites located in Washington County. Leaking underground storage tanks, site remediation projects, closed landfills and active solid waste facilities from the Rhode Island Department of Environmental Management. 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.