How does Wailuku's water compare to the national average?

The USA national average is 151 mg/L. Wailuku (≈ 120–179 mg/L) is 1 mg/L softer than average.

Wailuku Water Hardness & Quality Report (2026)

Water Hardness

hard

~120–179 mg/L

Hard

estimated · not lab-verified

Source

reservoir

pH Level

7.7

neutral = 7.0

Lead

0.002 mg/L

✓ Below action level

TDS

57 mg/L

Est. Daily Cost

$0.40

energy & soap waste

Source: See methodology section below · Updated 2026

hard~120–179 mg/LHard · est.

0–60

mg/L

Soft

61–120

mg/L

Moderately Hard

121–180

mg/L

Hard

180+

mg/L

Very Hard

Appliance Damage Report

In Wailuku, your appliances are currently losing 20% efficiency due to mineral buildup.

Appliance	In Wailuku	Soft Water City	Efficiency Loss
Kettle	6.8 yrs	8.5 yrs	-20%
Washing Machine	9.6 yrs	12 yrs	-20%
Water Heater	12 yrs	15 yrs	-20%

Regional Water Comparison

How Wailuku compares to its nearest neighbours

City	Hardness	PFAS (ppt)	Risk	Source
▶ Wailuku, Hawaii	≈ 120–179 mg/L	0 ppt	🟠 Hard	reservoir
Kahului, Hawaii	≈ 0–60 mg/L	1 ppt	🟢 Soft	groundwater
Kihei, Hawaii	≈ 0–60 mg/L	0.7 ppt	🟢 Soft	groundwater
Lahaina, Hawaii	≈ 0–60 mg/L	1 ppt	🟢 Soft	groundwater
Hawai'i Kai, Hawaii	≈ 0–60 mg/L	1.2 ppt	🟢 Soft	groundwater

National Benchmark

How Wailuku compares to the USA average

Benchmark	Hardness	Appliance Risk
▶ Wailuku	≈ 120–179 mg/L	🟠 Moderate
USA National Avg	151 mg/L	🟠 Moderate
Scarsdale Top Rated	0.02 mg/L	🟢 None

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What Makes Wailuku's Water Unique?

Local geology and source profile

Source: ReservoirTDS: 57 mg/LpH: 7.7

The Maui County Department of Water Supply provides water to Wailuku and other Central Maui communities. Its primary source is groundwater drawn from the Iao Aquifer, located beneath the West Maui Mountains. This aquifer receives its recharge from rainfall that filters through the volcanic landscape. A small amount of filtered surface water is also blended into the supply at the Iao Water Treatment Facility. Here, the water undergoes disinfection before it is distributed to households throughout the service area.

The Iao Aquifer is a substantial basal groundwater system, drawing its water from the West Maui Mountains watershed. As water percolates through the layers of volcanic rock and ancient coral limestone, it interacts with these mineral-rich geological formations. This natural process, influenced by Maui's volcanic history, imbues the water with a moderately mineralized quality, characterized by the presence of dissolved calcium and magnesium.

This water's moderate hardness means you might notice some scale buildup in appliances like coffee makers, dishwashers, and water heaters, which can affect their efficiency over time. You may also find that laundry doesn't feel quite as soft as usual. To combat scale, regularly flush your hot water systems and clean out appliance aerators. For those who prefer softer water and want to maximize the lifespan of their appliances, installing a water softener is a good option.

Geology & Source: Iao Aquifer; volcanic lava, coral limestone, and basaltic rock contribute to moderate mineral content and hardness

Other Hawaii Water Reports

Kahului

≈ 0–60 mg/L

🟢 Soft

Kihei

≈ 0–60 mg/L

🟢 Soft

Lahaina

≈ 0–60 mg/L

🟢 Soft

Hawai'i Kai

≈ 0–60 mg/L

🟢 Soft

Report an Issue

Notice an error or missing data? Help us keep this page accurate. If you spot incorrect water hardness, outdated utility info, or missing details, please let us know.

All reports are reviewed by our team. Thank you for supporting data quality!

Frequently Asked Questions

Is Wailuku's water safe to drink?

Yes. Wailuku's water meets all federal safety standards. The hardness is ≈ 120–179 mg/L (Hard), which is safe to drink. High hardness affects appliances and taste, but poses no health risk.

Do I need a water softener in Wailuku?

At ≈ 120–179 mg/L (Hard), Wailuku's water will cause significant limescale on kettles, washing machines, and water heaters. A water softener or descaler is strongly recommended to extend appliance lifespan and reduce energy bills by up to 20%.

How does Wailuku compare to the USA average?

The USA national average is 151 mg/L. Wailuku (≈ 120–179 mg/L) is 1 mg/L below the national average. The softest major city is Scarsdale at just 0.02 mg/L.

Data Sources & Methodology

Water quality data for Wailuku is derived from geographic and geological modelling of the surrounding region. No federal monitoring station data was available for this location.

Estimated

Water Hardness

Modelled estimate based on state-level USGS geological survey data for this region. No direct USGS Water Quality Portal measurement was matched to this city — the value reflects a statistical range calibrated to the state's dominant rock types and typical source water characteristics.

Estimated

Estimated from regional geology and source water characteristics. pH is correlated with water hardness and local bedrock — values may differ from utility-reported figures.

Estimated

TDS — Total Dissolved Solids

Estimated using a derived ratio from water hardness and regional conductance profiles. TDS in natural water correlates strongly with total mineral content including hardness ions.

Measured

PFAS — Perfluoroalkyl and Polyfluoroalkyl Substances

EPA UCMR5 (5th Unregulated Contaminant Monitoring Rule, 2023–2025) — sum of PFAS compounds detected at the public water system serving this city. A value of 0 indicates the system was sampled with no detection above reporting limits.

Modelled

Lead

Modelled estimate based on the EPA Lead and Copper Rule 90th-percentile tap-sample methodology. No publicly available per-city lead dataset with sufficient national coverage exists. Values are a conservative baseline derived from city population tier and infrastructure age — all estimates are maintained below the EPA action level of 0.015 mg/L.

Calculated

Appliance Lifespan

Calculated from water hardness using a linear degradation model. Baseline lifespans represent soft-water performance (kettle: 8.5 yrs, washing machine: 12.0 yrs, water heater: 15.0 yrs). Hard water mineral scale progressively reduces operational life in direct proportion to hardness concentration.