San Carlos, CA water hardness

Tap water hardness
33mg/L
1.9gpg
Soft

Reported by City of Redwood City · October 2025

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

San Carlos water measures 33 mg/L (1.9 gpg) of hardness, soft by USGS standards. The number comes from City of Redwood City, dated October 2025.

San Carlos 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 32Woodside: 32 mg/LWoodside 32Foster City: 33 mg/LFoster City 33San Mateo: 35 mg/LSan Mateo 35Hillsborough: 36 mg/LHillsborough 36Belmont: 37 mg/LBelmont 37Menlo Park: 46 mg/LMenlo Park 46Stanford: 146 mg/LStanford 146San Carlos 33mg/L as calcium carbonate060120180240300360+CA 121Redwood City: 32 mg/LRedwood Ci. 32North Fair Oaks: 32 mg/LNorth Fair. 32Woodside: 32 mg/LWoodside 32Foster City: 33 mg/LFoster City 33San Mateo: 35 mg/LSan Mateo 35Belmont: 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

At 33 mg/L, San Carlos is 88 mg/L below the typical California figure of 121. Of the 10 nearest cities we track, 4 have softer water and 5 have harder. The range nearby runs from 31 mg/L in Burlingame to 146 in Stanford.

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 San Carlos's water system

City of Redwood City · PWSID CA4110022

No health-based violations since 2016

Serves about 90,043 people from surface water.

Health-based
0
Monitoring or reporting
0
Open now
0

TapWaterData ties San Carlos to this system. EPA's service-area records do not name San Carlos, so check the utility printed on your water bill.

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 San Carlos 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 San Carlos 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 San Carlos water system had EPA violations?

EPA records show no health-based violations for City of Redwood City since 2016.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (utility report, October 6, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.