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

The USA national average is 151 mg/L. Kaimuki (≈ 0–59 mg/L) is 121 mg/L softer than average.

Kaimuki Water Hardness & Quality Report (2026)

Water Hardness

soft

~0–59 mg/L

Soft

estimated · not lab-verified

Source

groundwater

pH Level

7.4

neutral = 7.0

Lead

0.005 mg/L

✓ Below action level

TDS

119.8 mg/L

Est. Daily Cost

$0.08

energy & soap waste

Source: See methodology section below · Updated 2026

soft~0–59 mg/LSoft · 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 Kaimuki, your appliances are currently losing 4% efficiency due to mineral buildup.

Appliance	In Kaimuki	Soft Water City	Efficiency Loss
Kettle	8.2 yrs	8.5 yrs	-4%
Washing Machine	11.5 yrs	12 yrs	-4%
Water Heater	14.4 yrs	15 yrs	-4%

Regional Water Comparison

How Kaimuki compares to its nearest neighbours

City	Hardness	PFAS (ppt)	Risk	Source
▶ Kaimuki, Hawaii	≈ 0–59 mg/L	1 ppt	🟢 Soft	groundwater
Diamond Head / Kapahulu / Saint Louis Heights, Hawaii	≈ 0–60 mg/L	1.3 ppt	🟢 Soft	groundwater
Mo'ili'ili, Hawaii	≈ 120–179 mg/L	1.4 ppt	🟠 Hard	groundwater
McCully - Moiliili, Hawaii	≈ 0–60 mg/L	0.7 ppt	🟢 Soft	groundwater
Waikiki, Hawaii	≈ 0–60 mg/L	0.7 ppt	🟢 Soft	groundwater

National Benchmark

How Kaimuki compares to the USA average

Benchmark	Hardness	Appliance Risk
▶ Kaimuki	≈ 0–59 mg/L	🟢 None
USA National Avg	151 mg/L	🟠 Moderate
Scarsdale Top Rated	0.02 mg/L	🟢 None

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What Makes Kaimuki's Water Unique?

Local geology and source profile

Source: GroundwaterTDS: 119.8 mg/LpH: 7.4

Kaimuki is served by the Board of Water Supply (BWS), which provides drinking water to Oahu and surrounding areas. The utility sources its supply primarily from groundwater reserves tapped from Oahu's volcanic aquifer system. BWS operates multiple treatment facilities and distribution infrastructure across the island to serve residential, commercial, and industrial customers throughout the Kaimuki area. The utility reports that Oahu's water meets or exceeds EPA and Hawaii Department of Health standards, with ongoing monitoring ensuring safe tap water for all customers.

The Kaimuki water supply is part of Oahu's broader watershed system, characterized by Quaternary basaltic volcanic formations. These porous lava flows form the primary aquifer, allowing groundwater to percolate through layers of basalt. The volcanic geology naturally filters water and contributes to the soft water character typical of Hawaiian islands, with minimal dissolved mineral content compared to limestone or chalk-based aquifers found on continental landmasses.

As a soft water supply, Kaimuki residents experience minimal scaling in appliances and plumbing fixtures. Water heaters, dishwashers, and washing machines typically require less maintenance than in hard-water regions. Soap and detergents lather more effectively, and mineral buildup on fixtures is uncommon. Most households do not require water softening systems. The Board of Water Supply does not routinely report water hardness, but the volcanic filtration process and strict monitoring ensure tap water meets all regulatory standards for contaminants including lead and copper.

Geology & Source: Oahu volcanic aquifer system — Quaternary basaltic lava flows; porous basalt allows natural filtration; minimal calcium and magnesium dissolution from volcanic rock produces soft water typical of Hawaiian islands

Other Hawaii Water Reports

Diamond Head / Kapahulu / Saint Louis Heights

≈ 0–60 mg/L

🟢 Soft

Mo'ili'ili

≈ 120–179 mg/L

🟠 Hard

McCully - Moiliili

≈ 0–60 mg/L

🟢 Soft

Waikiki

≈ 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 Kaimuki's water safe to drink?

Yes. Kaimuki's water meets all federal safety standards. The hardness is ≈ 0–59 mg/L (Soft), which is safe to drink. High hardness affects appliances and taste, but poses no health risk.

Do I need a water softener in Kaimuki?

Kaimuki's water is soft at ≈ 0–59 mg/L. A water softener is generally not necessary, though a carbon filter can improve taste and remove any remaining chlorine.

How does Kaimuki compare to the USA average?

The USA national average is 151 mg/L. Kaimuki (≈ 0–59 mg/L) is 121 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 Kaimuki 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.