Hard water in Walnut, CA
Reported by Suburban Water Systems-San Jose · September 2025
- CA typical
- 121 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
The water in Walnut carries roughly 210 mg/L of dissolved calcium and magnesium, or 12.3 grains per gallon. That is very hard water. The number comes from Suburban Water Systems-San Jose, dated September 2025. Reports for this system disagree, with values from 210 to 275 mg/L.
Walnut sits 89 mg/L above the typical California figure of 121. Of the 10 nearest cities we track, 7 have softer water and 3 have harder. The range nearby runs from 112 mg/L in Citrus to 275 in Charter Oak.
What 210 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 210 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 × 12.3 gpg = 2,768 grains a day. A 24,000-grain unit regenerates about every 8 days.
EPA record for Walnut's water system
No health-based violations since 2016
Serves about 170,523 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 1
- Open now
- 0
TapWaterData ties Walnut to this system. EPA's service-area records do not name Walnut, 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 Walnut water hard?
Yes. It measures about 210 mg/L (12.3 grains per gallon), which the USGS classes as very hard.
What is the water hardness in Walnut in grains per gallon?
About 12.3 gpg. One grain per gallon equals 17.1 mg/L, so 210 mg/L divided by 17.1 gives 12.3.
What size water softener do I need in Walnut?
For 3 people using 75 gallons each per day, 12.3 gpg works out to about 2,768 grains a day. A 24,000-grain softener covers that with a regeneration about every 8 days.
Has the Walnut water system had EPA violations?
EPA records show no health-based violations for Suburban Water Systems-San Jose since 2016. There were also 1 monitoring or reporting violation, which are about late or missing tests and notices.
Nearby cities
- South San Jose Hills208 mg/LVery hard
- Diamond Bar153 mg/LHard
- West Covina170 mg/LHard
- Covina167 mg/LHard
- Valinda223 mg/LVery hard
- Charter Oak275 mg/LVery hard
- Rowland Heights160 mg/LHard
- San Dimas275 mg/LVery hard
- Pomona138 mg/LHard
- Citrus112 mg/LModerately hard
Hardness data: TapWaterData US Water Hardness (utility report, September 29, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.