San Mateo Water Hardness & Quality Report (2026)
Water Hardness
2.4 grains per gallon
Source
mixed
pH Level
7.2
neutral = 7.0
Lead
0.003 mg/L
✓ Below action level
TDS
85.1 mg/L
Est. Daily Cost
$0.11
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 San Mateo, your appliances are currently losing 5% efficiency due to mineral buildup.
| Appliance | In San Mateo | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 8.3 yrs | 8.5 yrs | -2% |
| Washing Machine | 12.1 yrs | 12 yrs | — |
| Water Heater | 14 yrs | 15 yrs | -7% |
Regional Water Comparison
How San Mateo compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ San Mateo, California | 40.5 mg/L | 3.2 ppt | 🟢 Soft | mixed |
| Burlingame, California | 131.5 mg/L | 5.9 ppt | 🟠 Hard | mixed |
| Foster City, California | 143 mg/L | 6.2 ppt | 🟠 Hard | mixed |
| Belmont, California | 176 mg/L | 7.1 ppt | 🟠 Hard | mixed |
| Millbrae, California | 126.5 mg/L | 5.7 ppt | 🟠 Hard | mixed |
National Benchmark
How San Mateo compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ San Mateo | 40.5 mg/L | 🟢 None |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes San Mateo's Water Unique?
Local geology and source profile
San Mateo, California, in the heart of San Mateo County on the San Francisco Bay Peninsula, receives its municipal water supply from the San Francisco Public Utilities Commission (SFPUC) through the Hetch Hetchy Regional Water System, delivering Tuolumne River water from Hetch Hetchy Reservoir in Yosemite National Park via the Hetch Hetchy Aqueduct, supplemented by local Peninsula Watershed storage at Crystal Springs Reservoir (across the San Andreas Fault) and the San Andreas Reservoir in San Mateo County. The city also receives SFPUC-managed supply through the Hetch Hetchy distribution main serving the Peninsula. Water hardness measures 40.5 mg/L — classified as soft.
San Mateo's soft supply reflects the dominance of Hetch Hetchy Aqueduct water and local Peninsula Watershed supply — both very soft California sources. Hetch Hetchy water derives from Tuolumne River snowmelt originating in the Tuolumne Batholith (Cretaceous granodiorite) and associated Sierra metamorphic belt. The Peninsula Watershed catchments drain the Santa Cruz Mountains terrain: the Purisima Formation (Pliocene mudstone and sandstone), Santa Cruz Mudstone, and older Monterey Formation (siliceous shale) — all siliceous, low-calcium marine sedimentary sequences. Both the SFPUC mountain source water and the Peninsula catchment produce consistently soft rainfall-derived supply in San Mateo County.
With hardness at 40.5 mg/L, San Mateo residents enjoy very soft water with essentially no scale challenges. Soap lathers extremely well. Faucet aerators and showerheads rarely need descaling. Dishwashers produce spotless glassware. SFPUC consistently delivers water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.
Geology & Source: Reservoir supply from the Hetch Hetchy Aqueduct (Tuolumne River, Yosemite) and Peninsula Watershed (Crystal Springs Reservoir, San Andreas Reservoir) via the San Francisco Public Utilities Commission (SFPUC) — Tuolumne River Sierra Nevada granodiorite snowmelt and Santa Cruz Mountains Purisima Formation sandstone catchment deliver very soft supply at 40.5 mg/L on the San Mateo County Peninsula.