Maui's water comes from one of the most beautiful sources on Earth — volcanic aquifers fed by 300 to 400 inches of annual rainfall on the windward slopes of Haleakalā and the West Maui Mountains. By the time that rain reaches the deep groundwater layers, it has been filtered through hundreds of feet of porous lava rock, often for decades. In its natural state, this is some of the purest source water in the world.
And yet, by the time it reaches your tap, it's a different story.
This article is not designed to scare you. It's designed to give you the truth — sourced directly from the EWG Tap Water Database, the U.S. Geological Survey, and Maui Department of Water Supply public reports — about what is actually present in our water in 2026, why it's there, and what it means for the people who drink it, shower in it, and raise families with it.
The legacy nobody talks about: plantation-era pesticides
From the 1940s through the 1980s, sugar and pineapple plantations covered much of central Maui. To control nematodes — microscopic worms that destroyed crop roots — growers fumigated the soil with industrial chemicals at scales that are difficult to imagine today. Two of those chemicals, in particular, are still showing up in our wells.
DBCP — banned in 1977, still in our water
1,2-Dibromo-3-chloropropane, known as DBCP, was banned in 1977 after it was linked to male sterility in workers who handled it. Nearly fifty years later, it is still being detected in wells across the Pa‘ia and Iao Aquifers — sometimes at levels hundreds of times above the EWG health guideline.
The reason DBCP persists is geological. Once it leaches into groundwater, it bonds with subsurface materials and slowly migrates through aquifers for decades. The chemical that was sprayed in the 1960s is the chemical we drink today.
1,2,3-Trichloropropane (TCP) — Hawai‘i has some of the highest levels in America
Originally an industrial impurity in the same nematocides used on Maui's plantations, 1,2,3-TCP is a probable human carcinogen that the EPA classifies as one of the most concerning groundwater contaminants in the western United States. Hawai‘i has some of the highest documented levels in the country.
The volcanic legacy: arsenic, naturally and otherwise
Arsenic occurs naturally in volcanic soils. As rainwater percolates through the deep basalt layers of Maui's mountains, it picks up trace amounts of arsenic from the rock itself. Decades of agricultural runoff — particularly from arsenic-based pesticides used widely before the 1980s — have concentrated this further in some aquifers.
Arsenic exposure is one of the slowest, quietest health risks in modern drinking water. It does not change the taste, smell, or color of water. It accumulates in the body over years.
The chemicals that don't go away: chlorine byproducts & PFAS
Once Maui's groundwater reaches the municipal treatment plants, chlorine is added to kill bacteria. This is necessary — without it, microbial contamination would be far more dangerous than what chlorine creates downstream. But chlorine reacts with naturally-occurring organic matter to form a class of compounds called disinfection byproducts — including trihalomethanes (TTHMs) and haloacetic acids (HAAs).
Disinfection byproducts have been linked to bladder cancer, miscarriage, and developmental issues in children. They are particularly concentrated at the end of long distribution pipes — meaning households farther from the treatment plant tend to receive higher levels.
PFAS — the "forever chemicals"
Per- and polyfluoroalkyl substances, or PFAS, have earned the nickname "forever chemicals" because they do not break down in nature. They were used for decades in firefighting foam, non-stick coatings, and waterproof materials. They are now showing up in groundwater and drinking water across the United States — including in Hawai‘i, where firefighting training sites and military installations have been documented sources.
The EPA has set new federal limits on PFAS in drinking water for the first time, taking effect in 2024-2027. Most water utilities are still testing and developing remediation plans. In the meantime, the only reliable household defense against PFAS is filtration — specifically, activated carbon and reverse osmosis.
What makes PFAS particularly difficult is that they bioaccumulate. Each glass of contaminated water adds to a body burden that the human system cannot effectively clear.
What the post-Lahaina fire context changed
The 2023 Lahaina fire raised serious questions about water quality in the impacted zones. When fire burns through plastic plumbing, melted PVC, polybutylene, and polyethylene pipes leach benzene, vinyl chloride, and other volatile organic compounds into the water lines. The Hawai‘i Department of Health issued unsafe water advisories for parts of West Maui that lasted for many months as the system was tested and remediated.
For homes that were not destroyed but received water through partially-impacted infrastructure, the question of long-term water quality remains open. Many West Maui homeowners have asked: is the water in my home truly safe again? The honest answer is that without testing your specific home's water, you cannot know.
What this means for your home
It would be easy to read this and conclude that Maui's water is dangerous. That's not the right takeaway. Maui's municipal water meets federal Safe Drinking Water Act standards. The county departments work hard, and they're transparent — the data above comes from their own publicly released reports, supplemented by EWG and USGS independent testing.
The right takeaway is more nuanced: federal standards are decades out of date for many of these contaminants, set in eras when the science was less mature and the political will to enforce stricter standards did not exist. The EWG health guidelines used in this article are based on current peer-reviewed science about cancer risk, neurological effects, and reproductive health — not 1980s-era regulatory floors.
If you live in Maui and want clean water, you have three real options:
- Bottled water. Expensive, environmentally harmful, often not meaningfully cleaner than tap (much bottled water is filtered municipal water with a label), and useless for showering or laundry — where most household water exposure actually occurs.
- Pitcher or single-tap filter. Removes some chlorine and improves taste. Does very little against DBCP, TCP, arsenic, PFAS, or disinfection byproducts. Does nothing for the water you shower or bathe in.
- Whole-home filtration. A multi-stage system installed at your home's main water line. Properly designed, it removes the contaminants discussed in this article from every tap, every shower, every appliance — and re-mineralizes the water so it nourishes rather than depletes.
How to know what's actually in your water
The contaminant data in this article reflects regional averages. Your specific home — depending on which aquifer feeds it, which distribution line carries it, how long the water has been sitting in your pipes, and what materials your plumbing is made of — may have meaningfully different results.
The only way to truly know what's in your water is to test it. Haven offers a free in-home water test for Maui and O‘ahu households: up to eight live measurements right at your sink, with each result walked through in plain language. You see exactly what's flowing through your taps. There's no charge, no obligation, and no follow-up sales pressure.