Hard water in Sunnyvale, CA

Tap water hardness
298mg/L
17.4gpg
Very hard

Reported by City of Sunnyvale · October 2025

CA typical
121 mg/L
EPA health violations since 2016
0
Softener for 3 people
32k grain
Data
Utility report

Sunnyvale water measures 298 mg/L (17.4 gpg) of hardness, very hard by USGS standards. The number comes from City of Sunnyvale, dated October 2025.

Sunnyvale on the hardness scale, with nearby cities
060120180240300360+CA typical 121Palo Alto: 29 mg/LPalo Alto 29Milpitas: 49 mg/LMilpitas 49Newark: 65 mg/LNewark 65Mountain View: 134 mg/LMountain View 134Stanford: 146 mg/LStanford 146Saratoga: 178 mg/LSaratoga 178Cupertino: 186 mg/LCupertino 186Santa Clara: 248 mg/LSanta Clara 248Los Altos Hills: 274 mg/LLos Altos Hills 274Los Altos: 298 mg/LLos Altos 298Sunnyvale 298mg/L as calcium carbonate060120180240300360+CA 121Palo Alto: 29 mg/LPalo Alto 29Mountain View: 134 mg/LMountain V. 134Cupertino: 186 mg/LCupertino 186Santa Clara: 248 mg/LSanta Clara 248Los Altos Hills: 274 mg/LLos Altos. 274Los Altos: 298 mg/LLos Altos 298298 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 298 mg/L, Sunnyvale 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 Los Altos.

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.

Softener size for Sunnyvale

3 people × 75 gallons a day × 17.4 gpg = 3,922 grains a day. A 32,000-grain unit regenerates about every 8 days.

Size it for your household

EPA record for Sunnyvale's water system

City of Sunnyvale · PWSID CA4310014

No health-based violations since 2016

Serves about 157,566 people from surface water.

Health-based
0
Monitoring or reporting
0
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 Sunnyvale 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 Sunnyvale 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 Sunnyvale?

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 Sunnyvale water system had EPA violations?

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

Nearby cities

All 515 cities in California

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.