Hard water in Los Altos, CA
Reported by CWSC Los Altos Suburban · October 2025
- CA typical
- 121 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 32k grain
- Data
- Utility report
The water in Los Altos carries roughly 298 mg/L of dissolved calcium and magnesium, or 17.4 grains per gallon. That is very hard water. The number comes from CWSC Los Altos Suburban, dated October 2025.
At 298 mg/L, Los Altos is 177 mg/L above the typical California figure of 121. None of the 10 nearest cities we track has harder water. The range nearby runs from 29 mg/L in Palo Alto to 298 in Sunnyvale.
What 298 mg/L means at home
Scale forms fast here. Kettles and coffee makers need regular descaling, and showerheads clog unless you clean them.
Tank water heaters collect mineral sediment that insulates the water from the burner, so flushing the tank matters more than usual.
Dishes and glass shower doors spot easily. Soap scum and a dull film on hair or laundry are common complaints.
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
At 298 mg/L most of the trouble is scale, and only a few things deal with it.
Ion-exchange water softener
The standard whole-house fix. It swaps calcium and magnesium for sodium or potassium and needs salt plus a drain. Size it with the calculator below.
Salt-free conditioner
No salt and no drain line. It changes how minerals form scale instead of removing them, so water still tests hard.
Reverse osmosis or carbon filter
Under-sink reverse osmosis removes minerals from drinking water only. Plain carbon filters improve taste but do not soften.
3 people × 75 gallons a day × 17.4 gpg = 3,922 grains a day. A 32,000-grain unit regenerates about every 8 days.
EPA record for Los Altos's water system
No health-based violations since 2016
Serves about 63,559 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 0
- Open now
- 0
TapWaterData ties Los Altos to this system. EPA's service-area records do not name Los Altos, 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 Los Altos water hard?
Yes. It measures about 298 mg/L (17.4 grains per gallon), which the USGS classes as very hard.
What is the water hardness in Los Altos in grains per gallon?
About 17.4 gpg. One grain per gallon equals 17.1 mg/L, so 298 mg/L divided by 17.1 gives 17.4.
What size water softener do I need in Los Altos?
For 3 people using 75 gallons each per day, 17.4 gpg works out to about 3,922 grains a day. A 32,000-grain softener covers that with a regeneration about every 8 days.
Has the Los Altos water system had EPA violations?
EPA records show no health-based violations for CWSC Los Altos Suburban since 2016.
Nearby cities
- Los Altos Hills274 mg/LVery hard
- Mountain View134 mg/LHard
- Palo Alto29 mg/LSoft
- Sunnyvale298 mg/LVery hard
- Cupertino186 mg/LVery hard
- Stanford146 mg/LHard
- Santa Clara248 mg/LVery hard
- Saratoga178 mg/LHard
- Menlo Park46 mg/LSoft
- North Fair Oaks32 mg/LSoft
Hardness data: TapWaterData US Water Hardness (utility report, October 7, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.