San Carlos Water Hardness & Quality Report (2026)
Water Hardness
9.5 grains per gallon
Source
mixed
pH Level
8.1
neutral = 7.0
Lead
0.008 mg/L
✓ Below action level
TDS
487.8 mg/L
Est. Daily Cost
$0.43
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 Carlos, your appliances are currently losing 22% efficiency due to mineral buildup.
| Appliance | In San Carlos | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 4.2 yrs | 8.5 yrs | -51% |
| Washing Machine | 7.6 yrs | 12 yrs | -37% |
| Water Heater | 9.1 yrs | 15 yrs | -39% |
Regional Water Comparison
How San Carlos compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ San Carlos, California | 163 mg/L | 6.8 ppt | 🟠 Hard | mixed |
| Belmont, California | 176 mg/L | 7.1 ppt | 🟠 Hard | mixed |
| Redwood City, California | 178 mg/L | 7.2 ppt | 🟠 Hard | mixed |
| Foster City, California | 143 mg/L | 6.2 ppt | 🟠 Hard | mixed |
| North Fair Oaks, California | 69.5 mg/L | 4 ppt | 🟡 Moderately Hard | mixed |
National Benchmark
How San Carlos compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ San Carlos | 163 mg/L | 🟠 Moderate |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes San Carlos's Water Unique?
Local geology and source profile
San Carlos, California, in San Mateo County — a major San Francisco Bay Area mid-Peninsula community (San Carlos is a significant San Mateo County city — a popular mid-Peninsula community known for its charming Laurel Street downtown (one of the most attractive small downtown corridors on the Peninsula — with independent restaurants, boutique shops, and a lively pedestrian character), strong public schools (San Carlos School District is one of the most highly regarded K-8 school districts in the Bay Area), and excellent location between San Francisco and Silicon Valley; San Carlos Airport (San Carlos Airport — KSQL — is a Caltrans Division of Aeronautics airport and one of the few small general aviation airports remaining on the Peninsula)), a diverse San Mateo County community with a primarily affluent Chinese-American, professional tech worker, and established Peninsula family population, adjacent to Redwood City and Belmont in the central Peninsula corridor — draws its municipal water supply via California Water Service. Water hardness in San Carlos measures 163 mg/L — classified as hard.
San Carlos's hard supply — notably higher than pure Hetch Hetchy values — reflects CalWater's mid-Peninsula supply blending with local groundwater. The CalWater distributes SFPUC Hetch Hetchy and local groundwater supply to the mid-Peninsula San Carlos zone, producing the hard 163 mg/L.
At 163 mg/L, San Carlos residents face regular hard water challenges. Monthly descaling is recommended. California Water Service consistently delivers water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.
Geology & Source: Imported supply from the Hetch Hetchy Reservoir (Tuolumne River) via the California Water Service (SFPUC supply) — the San Mateo County mid-Peninsula San Carlos corridor (Sierra Nevada calcareous-poor granite — the extremely calcareous-poor Sierra Nevada Hetch Hetchy granite watershed; CalWater distribution with some supply blending); hard supply at 163 mg/L in San Mateo County.