Hillsborough Water Hardness & Quality Report (2026)
Water Hardness
5.6 grains per gallon
Source
mixed
pH Level
7.6
neutral = 7.0
Lead
0.004 mg/L
✓ Below action level
TDS
238.7 mg/L
Est. Daily Cost
$0.25
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 Hillsborough, your appliances are currently losing 13% efficiency due to mineral buildup.
| Appliance | In Hillsborough | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 6.4 yrs | 8.5 yrs | -25% |
| Washing Machine | 10.1 yrs | 12 yrs | -16% |
| Water Heater | 11.8 yrs | 15 yrs | -21% |
Regional Water Comparison
How Hillsborough compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Hillsborough, California | 95.5 mg/L | 4.8 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 |
| San Bruno, California | 162 mg/L | 6.8 ppt | 🟠 Hard | mixed |
National Benchmark
How Hillsborough compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Hillsborough | 95.5 mg/L | 🟡 Low |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Hillsborough's Water Unique?
Local geology and source profile
Hillsborough, California, in San Mateo County — an affluent San Mateo County town adjacent to San Mateo and Burlingame on the San Francisco Peninsula — receives its water from California Water Service or SFPUC, drawing from the Hetch Hetchy aqueduct on the Tuolumne River through the north-central California distribution.
The soft 95.5 mg/L hardness and TDS of 238.7 mg/L reflect the San Mateo County Hetch Hetchy supply's soft character — the Cretaceous Sierra Nevada granodiorite and Jurassic metavolcanic rock are both highly insoluble crystalline formations contributing virtually no dissolved minerals to the pristine Tuolumne watershed, and the higher TDS relative to the source reflects distribution blending with Bay Area groundwater (compare San Mateo CA: 93/232 in San Mateo County comparable; Burlingame CA: 97/244 in San Mateo County comparable; Hillsborough consistent soft from the same San Mateo County Hetch Hetchy Sierra Nevada granitic supply). The Tuolumne watershed — Cretaceous Sierra Nevada granodiorite (insoluble — primary dilutant), Jurassic metavolcanic rock (insoluble — secondary dilutant), and Quaternary Sierra Nevada moraines (slightly calcareous — minimal TDS).
At 95.5 mg/L with TDS 239, Hillsborough's water is soft — minimal scale buildup. Annual descaling is appropriate. The PFAS level of 4.8 ppt is moderate — a certified drinking water filter is recommended. Review California Water Service's annual water quality report.
Geology & Source: Hillsborough in San Mateo County draws from the California Water Service on the Hetch Hetchy system (San Mateo County, north-central California) — the Tuolumne watershed drains Cretaceous Sierra Nevada granodiorite (insoluble) and Jurassic metavolcanic rock (insoluble) — California San Mateo County Hetch Hetchy Sierra Nevada granitic supply produces soft water at 95.5 mg/L with TDS 238.7 mg/L.