Hillsborough, CA water hardness

Tap water hardness
36mg/L
2.1gpg
Soft

Reported by California Water Service - San Mateo · October 2025

CA typical
121 mg/L
EPA health violations since 2016
0
Data
Utility report

Hillsborough water measures 36 mg/L (2.1 gpg) of hardness, soft by USGS standards. The number comes from California Water Service - San Mateo, dated October 2025.

Hillsborough on the hardness scale, with nearby cities
060120180240300360+CA typical 121Burlingame: 31 mg/LBurlingame 31Foster City: 33 mg/LFoster City 33San Carlos: 33 mg/LSan Carlos 33San Mateo: 35 mg/LSan Mateo 35Belmont: 37 mg/LBelmont 37Millbrae: 44 mg/LMillbrae 44San Bruno: 44 mg/LSan Bruno 44El Granada: 46 mg/LEl Granada 46South San Francisco: 64 mg/LSouth San Francisco 64Pacifica: 70 mg/LPacifica 70Hillsborough 36mg/L as calcium carbonate060120180240300360+CA 121Burlingame: 31 mg/LBurlingame 31Foster City: 33 mg/LFoster City 33San Mateo: 35 mg/LSan Mateo 35Belmont: 37 mg/LBelmont 37Millbrae: 44 mg/LMillbrae 44San Bruno: 44 mg/LSan Bruno 4436 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

Hillsborough sits 85 mg/L below the typical California figure of 121. Of the 10 nearest cities we track, 4 have softer water and 6 have harder. The range nearby runs from 31 mg/L in Burlingame to 70 in Pacifica.

What 36 mg/L means at home

Soap and shampoo lather with very little product. Kettles and showerheads stay mostly free of white crust.

Some people notice that soap feels slow to rinse off in soft water. That slippery feel is normal and harmless.

Hardness is not a health problem, and EPA sets no limit for it. It is a matter of scale and soap.

What to do about it

Nothing, as far as hardness goes. At 36 mg/L a softener would have almost nothing to remove.

Carbon filter

If the water tastes of chlorine, a pitcher or faucet carbon filter takes care of that. It does not change hardness.

EPA record for Hillsborough's water system

Town of Hillsborough · PWSID CA4110016

No health-based violations since 2016

Serves about 11,766 people from surface water.

Health-based
0
Monitoring or reporting
0
Open now
0

EPA lists Town of Hillsborough as the system serving Hillsborough. The hardness figure above comes from a different system's report, which TapWaterData uses for Hillsborough.

Health-based means a contaminant above its legal limit or a missed treatment step. Monitoring and reporting violations are late or missing tests and notices. Source: EPA ECHO, 2026Q3 export, violations with periods starting 2016 or later. Full EPA record.

Questions

Is Hillsborough water hard?

No. It measures about 36 mg/L (2.1 grains per gallon), which the USGS classes as soft.

What is the water hardness in Hillsborough in grains per gallon?

About 2.1 gpg. One grain per gallon equals 17.1 mg/L, so 36 mg/L divided by 17.1 gives 2.1.

Has the Hillsborough water system had EPA violations?

EPA records show no health-based violations for Town of Hillsborough since 2016.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (utility report, October 14, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.