Half Moon Bay Water Hardness & Quality Report (2026)
Water Hardness
6.9 grains per gallon
Source
mixed
pH Level
7.8
neutral = 7.0
Lead
0.005 mg/L
✓ Below action level
TDS
316.5 mg/L
Est. Daily Cost
$0.32
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 Half Moon Bay, your appliances are currently losing 16% efficiency due to mineral buildup.
| Appliance | In Half Moon Bay | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 5.7 yrs | 8.5 yrs | -33% |
| Washing Machine | 9.2 yrs | 12 yrs | -23% |
| Water Heater | 10.9 yrs | 15 yrs | -27% |
Regional Water Comparison
How Half Moon Bay compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Half Moon Bay, California | 118.5 mg/L | 5.5 ppt | 🟡 Moderately Hard | mixed |
| Burlingame, California | 131.5 mg/L | 5.9 ppt | 🟠 Hard | mixed |
| Millbrae, California | 126.5 mg/L | 5.7 ppt | 🟠 Hard | mixed |
| San Mateo, California | 40.5 mg/L | 3.2 ppt | 🟢 Soft | mixed |
| Pacifica, California | 98 mg/L | 4.9 ppt | 🟡 Moderately Hard | mixed |
National Benchmark
How Half Moon Bay compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Half Moon Bay | 118.5 mg/L | 🟡 Low |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Half Moon Bay's Water Unique?
Local geology and source profile
Half Moon Bay, California, in San Mateo County — a San Mateo County city adjacent to Pacifica and Redwood City on the Pacific Coast of the San Francisco Peninsula — receives its water from the SFPUC, drawing from Hetch Hetchy or San Andreas Lake (San Mateo County) through the San Francisco Peninsula distribution.
The moderately hard 118.5 mg/L hardness and TDS of 316.5 mg/L are harder than expected for the SFPUC Hetch Hetchy supply (typically 30-50 mg/L for SF proper) — reflecting Half Moon Bay's draw from the local San Mateo County coastal blended supply where the Cretaceous Franciscan calcareous contacts and coastal groundwater mixing contribute significant additional hardness over the pure Sierra Nevada granite supply. The Hetch Hetchy-San Andreas supply at San Mateo County — Cretaceous Franciscan Chert (insoluble — dilutant from Hetch Hetchy), Quaternary coastal alluvium (calcareous — primary hardness contributor from local blend), and Tertiary Santa Cruz Mudstone (calcareous — secondary TDS contributor).
At 118.5 mg/L with TDS 317, Half Moon Bay's water is moderately hard — scale builds in kettles and appliances over months, dishwashers benefit from rinse aid, and faucet aerators need periodic cleaning. Quarterly descaling is appropriate. The PFAS level of 5.5 ppt warrants a certified drinking water filter — the San Mateo County Peninsula industrial corridor contribute to Half Moon Bay's readings.
Geology & Source: Half Moon Bay in San Mateo County draws from the SFPUC on Hetch Hetchy or San Andreas Lake (San Mateo County, San Francisco Peninsula, California) — the Hetch Hetchy-San Andreas watershed drains Sierra Nevada granodiorite (insoluble) and Cretaceous Franciscan Chert (insoluble) — California San Mateo County SFPUC Hetch Hetchy Sierra-Franciscan insoluble supply produces moderately hard water at 118.5 mg/L with TDS 316.5 mg/L.