Hilo Water Hardness & Quality Report (2026)
Water Hardness
3.5 grains per gallon
Source
groundwater
pH Level
7.6
neutral = 7.0
Lead
0.007 mg/L
✓ Below action level
TDS
185.1 mg/L
Est. Daily Cost
$0.16
energy & soap waste
Source: USGS Water Quality Portal · Updated 2026
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 Hilo, your appliances are currently losing 8% efficiency due to mineral buildup.
| Appliance | In Hilo | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 7.6 yrs | 8.5 yrs | -11% |
| Washing Machine | 11.4 yrs | 12 yrs | -5% |
| Water Heater | 13.2 yrs | 15 yrs | -12% |
Regional Water Comparison
How Hilo compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Hilo, Hawaii | 60.5 mg/L | 1.2 ppt | 🟡 Moderately Hard | groundwater |
| Kihei, Hawaii | 22 mg/L | 0.7 ppt | 🟢 Soft | groundwater |
| Kahului, Hawaii | 40 mg/L | 1 ppt | 🟢 Soft | groundwater |
| Wailuku, Hawaii | 23 mg/L | 0.7 ppt | 🟢 Soft | groundwater |
| Hawai'i Kai, Hawaii | 56 mg/L | 1.2 ppt | 🟢 Soft | groundwater |
National Benchmark
How Hilo compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Hilo | 60.5 mg/L | 🟡 Low |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Hilo's Water Unique?
Local geology and source profile
Hilo, Hawaii, the Hawaii County seat on the Big Island (Hawaii Island) — the largest city on the Big Island of Hawaii, a culturally rich community with significant Native Hawaiian, Japanese-American, and Filipino-American populations, gateway to Hawaii Volcanoes National Park (active Kilauea and Mauna Loa volcanoes), one of the wettest cities in the United States (average annual rainfall exceeding 130 inches), and the setting for both the Merrie Monarch Festival (the world's premier hula competition) and the Pacific Tsunami Museum — draws its municipal water supply from the Wailuku River watershed and Mauna Kea basal aquifer via the Hawaii County Department of Water Supply (DWS). Water hardness in Hilo measures 60.5 mg/L — classified as moderately soft.
Hilo's moderate softness — slightly harder than Pearl City (32.5 mg/L) — reflects the Big Island's calcium-poor basalt geology with some marine aerosol influence. The Hilo basal aquifer draws from rainfall recharge on Mauna Loa and Mauna Kea (the Quaternary–Holocene tholeiitic basalt of the Big Island's shield volcanoes — calcium-poor tholeiitic ocean island basalt terrain). The Wailuku River watershed (draining the Mauna Kea saddle zone) provides additional very soft surface water. The moderate 60.5 mg/L at Hilo is slightly higher than Oahu's supplies due to marine aerosol calcium deposition on the windward Big Island and some older Hilo urban distribution infrastructure influence.
With hardness at 60.5 mg/L, Hilo residents enjoy moderately soft water. Hawaii County Department of Water Supply consistently delivers water meeting all Hawaii DOH and EPA Safe Drinking Water Act requirements.
Geology & Source: Groundwater from the Hawaii County (Hilo) Wailuku River aquifer and Mauna Kea–Mauna Loa basal aquifer via the Hawaii County Department of Water Supply (DWS) — the Hawaii County Hilo district (Quaternary–Holocene Mauna Loa and Mauna Kea Basalt lava aquifer — highest rainfall zone on the US Big Island); moderately soft supply at 60.5 mg/L — reflecting the Big Island's calcium-poor basalt volcanic terrain.