Hard water in Mountain View, CA
Reported by Contra Costa Water District · October 2025
- CA typical
- 121 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
Mountain View water measures 134 mg/L (7.9 gpg) of hardness, hard by USGS standards. The number comes from Contra Costa Water District, dated October 2025.
At 134 mg/L, Mountain View is 13 mg/L above 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 29 mg/L in Palo Alto to 298 in Los Altos.
What 134 mg/L means at home
Expect white crust on faucets and showerheads, plus spots on dishes that come out of the dishwasher.
Kettles collect scale quickly. Water heaters build up sediment at the bottom of the tank, which makes them work harder over time.
Soap and detergent need a little more to lather, and soap scum shows up in the tub.
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 134 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 × 7.9 gpg = 1,771 grains a day. A 24,000-grain unit regenerates about every 13 days.
EPA record for Mountain View's water system
No health-based violations since 2016
Serves about 81,340 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 0
- Open now
- 0
EPA lists City of Mountain View as the system serving Mountain View. The hardness figure above comes from a different system's report, which TapWaterData uses for Mountain View.
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 Mountain View water hard?
Yes. It measures about 134 mg/L (7.9 grains per gallon), which the USGS classes as hard.
What is the water hardness in Mountain View in grains per gallon?
About 7.9 gpg. One grain per gallon equals 17.1 mg/L, so 134 mg/L divided by 17.1 gives 7.9.
What size water softener do I need in Mountain View?
For 3 people using 75 gallons each per day, 7.9 gpg works out to about 1,771 grains a day. A 24,000-grain softener covers that with a regeneration about every 13 days.
Has the Mountain View water system had EPA violations?
EPA records show no health-based violations for City of Mountain View since 2016.
Nearby cities
- Los Altos298 mg/LVery hard
- Sunnyvale298 mg/LVery hard
- Palo Alto29 mg/LSoft
- Los Altos Hills274 mg/LVery hard
- Stanford146 mg/LHard
- Cupertino186 mg/LVery hard
- Santa Clara248 mg/LVery hard
- Menlo Park46 mg/LSoft
- Newark65 mg/LModerately hard
- 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.