Well water hardness in Maui County, Hawaii
9.9 gpg hard
Private wells in Maui County typically give hard water: the median well sampled by the U.S. Geological Survey has 9.9 gpg (170 mg/L as CaCO₃).
Wells differ a lot, even next door: one in ten sampled wells had less than 39 mg/L and one in ten more than 514 mg/L. The figure comes from 18 wells and 19 samples taken between 1980 and 2009 (half of them by 1989).
Most samples are older than ten years. Groundwater hardness comes from the rock the well is drilled into and changes slowly, but your own well can be quite different, so treat this as a regional indication and test your water.
What this hardness means for a well household
- Fast scale on taps, shower screens and kettle; white spots on glassware.
- Water heater: efficiency loss and element failures within years if unprotected.
- Dry skin and dull hair after showering are common.
- Softener recommended; jug or reverse osmosis for drinking.
How to test your well in Hawaii
Hardness is only one part of a well test. Federal health agencies advise every private well owner to test regularly:
- Test a private well every year for total coliform bacteria, nitrates, total dissolved solids and pH; test more often if young children, older adults or a pregnant or nursing person live in the home. (US EPA, Protect Your Home's Water)
- Test at least once a year and ask the local health department which other germs or chemicals matter where you live. (CDC, Guidelines for Testing Well Water)
- Have the well tested regularly for bacteriological and chemical contaminants by a lab certified or approved for the specific tests, and ask it to use EPA-approved drinking-water methods. (Hawaii Department of Health, Private Water Wells (rev. 2024-10-21))
Use a certified laboratory: Hawaii DOH, Certified or Approved Drinking Water Laboratories.
Hawaii has no regulation of private wells serving individual residences and no requirement for regular testing (Hawaii DOH, Private Water Wells).
If no local lab suits you, mail-in kits from certified labs test a wider panel at home; they cost more than a state or county lab.
Treating hard well water
Most households with hard well water install an ion-exchange softener. Test iron and manganese first: above about 0.3 mg/L iron a softener alone is not enough and an iron filter goes in front of it.
Nearby counties
FAQ
How hard is well water in Maui County, Hawaii?
The median well sampled by the USGS in Maui County has 9.9 gpg (170 mg/L as CaCO₃), which is hard. One in ten wells had less than 39 mg/L and one in ten more than 514 mg/L.
Is my own well the same?
Not necessarily. Hardness depends on the rock layer your well draws from and on its depth, so neighbouring wells can differ by a factor of two or more. Only a test of your own water tells you.
How often should I test my well in Hawaii?
Every year for coliform bacteria, nitrate, total dissolved solids and pH (EPA and CDC advice), and after floods, repairs or a change in taste or smell. Hardness, iron and manganese once, and again before you buy a softener.
Do I need a water softener for my well?
Recommended if you have a water heater, boiler or tankless unit: it saves repairs and detergent.
Where does this figure come from?
From 19 samples of 18 wells measured by the U.S. Geological Survey between 1980 and 2009, retrieved from the Water Quality Portal. We publish a county only when at least 10 wells were sampled.
Source and method
Computed by Water Hardness Atlas from USGS National Water Information System samples (characteristic "Hardness, Ca, Mg", sites of type well, samples since 1980), retrieved 2026-10-29 through the Water Quality Portal. For each well we take the median of its samples, then the median of all wells in the county; wells above 1,000 mg/L (oil, gas or mine brines) are left out. USGS data are in the U.S. public domain. Water Quality Portal query