Well water in Honolulu County, Hawaii
In Honolulu County, 3% of 237 tested well samples exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
15,234 test results across 14 contaminants from at least 203 wells, 1905 to 2026; chloride has the most at 13,969. Data refreshed September 3, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
What individual samples found
Each row summarizes every public sample for that contaminant inside Honolulu 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 1970 to 2024 | 237 | 99% | 1.07 | 20.8 | 10 mg/L EPA limit | |
| Fluoride 1970 to 2024 | 161 | 63% | 0.09 | 0.5 | 4 mg/L EPA limit | |
| Lead 1982 to 2024 | 95 | 44% | 0 | 2.29 | 15 ug/L EPA limit | |
| Arsenic 1982 to 2024 | 81 | 11% | 0 | 1 | 10 ug/L EPA limit | |
| Copper 1982 to 2024 | 81 | 94% | 0.002 | 0.014 | 1.3 mg/L EPA limit | |
| Uranium 1999 to 2024 | 69 | 13% | 0 | 0.18 | 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 | 13,969 | 100% | 200 | 54,000 | 250 mg/L nuisance level |
| Sodium 1970 to 2024 | no limit | 161 | 100% | 39.1 | 7,200 | 20 mg/L health guideline |
| Iron 1972 to 2024 | no limit | 146 | 39% | 0 | 610 | 300 ug/L nuisance level |
| Manganese 1972 to 2024 | no limit | 145 | 26% | 0 | 530 | 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 | 0%91 samples | 5%86 samples | 0%10 samples | 4%50 samples |
| Fluoride | 0%88 samples | 0%43 samples | n/a | 0%25 samples |
| Lead | 0%27 samples | 0%43 samples | n/a | 0%25 samples |
| Arsenic | 0%13 samples | 0%43 samples | n/a | 0%25 samples |
| Copper | 0%13 samples | 0%43 samples | n/a | 0%25 samples |
| Uranium | n/a | 0%43 samples | n/a | 0%25 samples |
Nitrate, fluoride, lead, arsenic, copper, uranium have held within a few points between the two most recent periods with enough samples.
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 (3% of 237 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 is widespread in local groundwater. It is mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Honolulu County
- 1Nitrate3% of 237 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 94% of local samples.
- 6FluorideDetected in 63% of local samples.
Test your Honolulu County 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 Honolulu County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
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
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.
Free, no obligation
Get on the list for a free in-home water test in Honolulu County
No water treatment company serves Honolulu 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 Honolulu County, and you get an email naming it first.
Common questions
Is there arsenic in well water in Honolulu County?
Arsenic was detected in 11% of 81 public well samples in Honolulu 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 high is radon in well water in Honolulu County?
The median radon level across 31 public samples in Honolulu County 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 Honolulu 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 Honolulu 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 Hawaii dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 15,234 samples in Honolulu 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.
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.