Foster City, CA water hardness

Tap water hardness
33mg/L
1.9gpg
Soft

Reported by Estero Municipal Improvement District · June 2025

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

The water in Foster City carries roughly 33 mg/L of dissolved calcium and magnesium, or 1.9 grains per gallon. That is soft water. The number comes from Estero Municipal Improvement District, dated June 2025.

Foster City on the hardness scale, with nearby cities
060120180240300360+CA typical 121Burlingame: 31 mg/LBurlingame 31Redwood City: 32 mg/LRedwood City 32North Fair Oaks: 32 mg/LNorth Fair Oaks 32San Carlos: 33 mg/LSan Carlos 33San Mateo: 35 mg/LSan Mateo 35Hillsborough: 36 mg/LHillsborough 36Belmont: 37 mg/LBelmont 37Millbrae: 44 mg/LMillbrae 44Hayward: 44 mg/LHayward 44Menlo Park: 46 mg/LMenlo Park 46Foster City 33mg/L as calcium carbonate060120180240300360+CA 121Burlingame: 31 mg/LBurlingame 31Redwood City: 32 mg/LRedwood Ci. 32San Carlos: 33 mg/LSan Carlos 33San Mateo: 35 mg/LSan Mateo 35Hillsborough: 36 mg/LHillsborou. 36Belmont: 37 mg/LBelmont 3733 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

Foster City sits 88 mg/L below the typical California figure of 121. Of the 10 nearest cities we track, 3 have softer water and 6 have harder. The range nearby runs from 31 mg/L in Burlingame to 46 in Menlo Park.

What 33 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 33 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 Foster City's water system

Estero Municipal Improvement District · PWSID CA4110021

No health-based violations since 2016

Serves about 36,556 people from surface water.

Health-based
0
Monitoring or reporting
1
Open now
0

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 Foster City water hard?

No. It measures about 33 mg/L (1.9 grains per gallon), which the USGS classes as soft.

What is the water hardness in Foster City in grains per gallon?

About 1.9 gpg. One grain per gallon equals 17.1 mg/L, so 33 mg/L divided by 17.1 gives 1.9.

Has the Foster City water system had EPA violations?

EPA records show no health-based violations for Estero Municipal Improvement District since 2016. There were also 1 monitoring or reporting violation, which are about late or missing tests and notices.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (utility report, June 30, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.