Well water in Hawaii
In Hawaii, 3% of 502 tested well samples exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
32,285 test results across 14 contaminants from at least 497 wells, 1905 to 2026; chloride has the most at 29,421. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 56,296 people in Hawaii get their drinking water from a private well, per USGS 2015 county water use.
Separately, the USGS national arsenic model estimates that 0% of the 56,296 people on private wells in Hawaii 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 Hawaii. 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 1970 to 2024 | 502 | 99% | 1.1 | 27 | 10 mg/L EPA limit | |
| Fluoride 1970 to 2024 | 420 | 78% | 0.1 | 0.8 | 4 mg/L EPA limit | |
| Arsenic 1980 to 2026 | 186 | 41% | 0 | 4.2 | 10 ug/L EPA limit | |
| Lead 1980 to 2026 | 179 | 50% | 0 | 11 | 15 ug/L EPA limit | |
| Copper 1980 to 2026 | 164 | 89% | 0.001 | 0.083 | 1.3 mg/L EPA limit | |
| Uranium 1989 to 2024 | 113 | 45% | 0 | 2.2 | 30 ug/L EPA limit | |
| Radium (226 + 228) 2000 | 56 | 70% | 0 | 0.04 | 5 pCi/L EPA limit | |
| Chloride 1905 to 2026 | no limit | 29,421 | 100% | 140 | 54,000 | 250 mg/L nuisance level |
| Sodium 1970 to 2026 | no limit | 442 | 100% | 46 | 9,120 | 20 mg/L health guideline |
| Iron 1972 to 2026 | no limit | 385 | 54% | 8.9 | 3,400 | 300 ug/L nuisance level |
| Manganese 1972 to 2026 | no limit | 384 | 38% | 0 | 1,160 | 300 ug/L health guideline |
| Radon 2000 | no limit | 31 | 100% | 100 | 400 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: PFOS (1), PFOA (1).
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 | 2%318 samples | 7%119 samples | 0%15 samples | 4%50 samples |
| Fluoride | 0%298 samples | 0%52 samples | 0%45 samples | 0%25 samples |
| Arsenic | 0%54 samples | 0%46 samples | 0%40 samples | 0%46 samples |
| Lead | 0%68 samples | 0%46 samples | 0%19 samples | 0%46 samples |
| Copper | 0%53 samples | 0%46 samples | 0%19 samples | 0%46 samples |
| Uranium | n/a | 0%46 samples | 0%40 samples | 0%25 samples |
Nitrate, fluoride, arsenic, lead, copper, uranium have held within a few points between the two most recent periods with enough samples.
What this means
The contaminants most often above their limit here are nitrate (3% of 502 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 and Iron 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 Hawaii
- 1Nitrate3% of 502 local samples were above the limit.
- 2Coliform bacteriaRecommended for every private well, every year.
- 3RadonMedian local reading is 100 pCi/L.
- 4ChlorideDetected in 100% of local samples.
- 5CopperDetected in 89% of local samples.
- 6FluorideDetected in 78% of local samples.
- 7IronDetected in 54% of local samples.
Test your Hawaii well for nitrate, coliform bacteria and radon
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 Hawaii: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Hawaii numbers, $29. Every line explained, ranked by what matters, with the fix for each.
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Send me the Hawaii report
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Official help in Hawaii
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 Water Wells (PDF), Hawaii Department of Health
- Drinking Water Certification Program, Hawaii Department of Health
Treatment that fits the local profile
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Chloride
Point-of-use reverse osmosis; Distillation
Systems we would look at first
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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.
Common questions
Is there arsenic in well water in Hawaii?
Arsenic was detected in 41% of 186 public well samples in Hawaii, 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 high is radon in well water in Hawaii?
The median radon level across 31 public samples in Hawaii was 100 pCi/L, with a high of 400 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Hawaii?
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 in Hawaii
1 counties have fewer than 30 public samples and are included in the Hawaii totals above rather than shown separately: Kalawao.
Want the numbers themselves? Download the Hawaii dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 32,285 samples in Hawaii. 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 56,296 people on private wells in Hawaii 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.
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.