Upcountry Maui Water Report
Compiled from EWG's Tap Water Database and the County of Maui Department of Water Supply's 2025 Water Quality Reports, covering the Makawao and Upper Kula systems. Your exact numbers can vary by address — book a consult and we'll confirm your specific system.
Three systems, one region
Upcountry Maui's water actually comes from three interconnected but separately managed systems — Makawao, Lower Kula, and Upper Kula. They share source protection and can send water to each other in emergencies, but day to day, they're kept apart for a specific reason.
Why Upcountry sees more boil water advisories
Makawao and Lower Kula disinfect with chlorine. Upper Kula disinfects with chloramine — a treatment better suited to its higher-organic-matter source water, since it forms fewer disinfection byproducts. The County keeps these two treatment types separate because mixing them creates water quality problems: chloramine breakdown can generate nitrates and encourage bacterial regrowth in pipes built for a different disinfectant. So when one system is down for maintenance or repairs and the other has to take its place, there can be a temporary gap in water quality that requires a boil water advisory.
This is exactly the kind of situation our filtration systems are built for — they reduce bacteria and viruses in addition to chlorine and chloramine, so your water stays protected through a boil advisory, not just on an ordinary day.
Disinfection Byproducts
Total Trihalomethanes (TTHMs)
Cancer riskWhat is this and where does it come from?
TTHMs form when chlorine reacts with naturally occurring organic matter in the water — a byproduct of the disinfection process itself, not contamination from an outside source.
Haloacetic Acids (HAA5)
Cancer riskWhat is this and where does it come from?
A group of five chemicals formed when chlorine or chloramine disinfects water. Increases cancer risk and may affect pregnancy with prolonged exposure.
Chloroform
Cancer riskWhat is this and where does it come from?
The most common of the trihalomethane group, formed as a byproduct of chlorine disinfection.
Bromodichloromethane
Cancer riskWhat is this and where does it come from?
One of the four trihalomethanes formed during disinfection. Linked to cancer risk and potential harm to fetal growth.
Dichloroacetic Acid
Cancer riskWhat is this and where does it come from?
One of five haloacetic acids formed during disinfection. Linked to cancer risk and harm to reproduction and child development.
Trichloroacetic Acid
Cancer riskWhat is this and where does it come from?
A haloacetic acid formed during disinfection. Linked to cancer risk and harm to reproduction and child development.
Dibromochloromethane
Cancer riskWhat is this and where does it come from?
One of the four trihalomethanes formed during disinfection.
Bromochloroacetic Acid
Cancer riskWhat is this and where does it come from?
A haloacetic acid formed during disinfection.
Dibromoacetic Acid
Cancer riskWhat is this and where does it come from?
A haloacetic acid formed during disinfection.
Bromoform
Cancer riskWhat is this and where does it come from?
One of the four trihalomethanes formed during disinfection.
Agricultural & Industrial Legacy
1,2,3-Trichloropropane (TCP)
Cancer riskWhat is this and where does it come from?
A potent carcinogen used historically as a soil fumigant in agricultural regions. Hawaiʻi regulates TCP even though the EPA does not.
DBCP (1,2-Dibromo-3-chloropropane)
Cancer & fertility riskWhat is this and where does it come from?
A pesticide fumigant banned in the 1970s after it was found to cause sterility in exposed male workers. Still detected in some Maui groundwater from past agricultural use.
Hexavalent Chromium
Cancer riskWhat is this and where does it come from?
A carcinogen that can come from industrial pollution or occur naturally in mineral deposits and groundwater.
Nitrate
Cancer & infant health riskWhat is this and where does it come from?
Enters water from fertilizer runoff, septic systems, and urban runoff. Can cause oxygen deprivation in infants and increases cancer risk.
Endocrine Disruptor
Chlorate
Thyroid functionWhat is this and where does it come from?
Forms as a byproduct of disinfection. Impairs thyroid function, making exposure most concerning during pregnancy and childhood — worth knowing about even at levels currently within guideline.
What this means for you
Your water meets every federal and state legal limit — the County's testing confirms both systems are in full compliance. But "legal" reflects standards that haven't been updated in nearly 20 years, not the latest independent health science. Several disinfection byproducts here are found at many times the health guideline set by EWG's scientists, even while comfortably under the legal limit. And the agricultural contaminants — TCP and DBCP especially — are remnants of Maui's plantation era that still turn up in testing today, worth filtering out even at levels currently within guideline.
What's in your pipes matters too. These results describe the water as it leaves the utility's system. On the way to your tap it can pick up lead, copper, or other metals from older city plumbing or from the pipes, fixtures, and solder in your own home. A utility's results can't see that, but testing your tap can.
Good news: no PFAS or fluoride
Both systems have tested negative for PFAS ("forever chemicals") since monitoring began in 2023, and Maui DWS has never added fluoride to Upcountry water.
Book Your Free Consult
We'll confirm which utility serves your address, walk through what your results mean, and recommend the right filtration for your home — no pressure, just answers.
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