Hard water in Altadena, CA
Reported by Pasadena Water and Power · October 2025
- CA typical
- 121 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
The water in Altadena carries roughly 234 mg/L of dissolved calcium and magnesium, or 13.7 grains per gallon. That is very hard water. The number comes from Pasadena Water and Power, dated October 2025.
At 234 mg/L, Altadena is 113 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 3 mg/L in La Crescenta-Montrose to 230 in Pasadena.
What 234 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 234 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 × 13.7 gpg = 3,078 grains a day. A 24,000-grain unit regenerates about every 7 days.
EPA record for Altadena's water system
No health-based violations since 2016
Serves about 165,448 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 0
- Open now
- 0
TapWaterData ties Altadena to this system. EPA's service-area records do not name Altadena, 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 Altadena water hard?
Yes. It measures about 234 mg/L (13.7 grains per gallon), which the USGS classes as very hard.
What is the water hardness in Altadena in grains per gallon?
About 13.7 gpg. One grain per gallon equals 17.1 mg/L, so 234 mg/L divided by 17.1 gives 13.7.
What size water softener do I need in Altadena?
For 3 people using 75 gallons each per day, 13.7 gpg works out to about 3,078 grains a day. A 24,000-grain softener covers that with a regeneration about every 7 days.
Has the Altadena water system had EPA violations?
EPA records show no health-based violations for Pasadena Water and Power since 2016.
Nearby cities
- Pasadena230 mg/LVery hard
- La Cañada Flintridge218 mg/LVery hard
- San Marino116 mg/LModerately hard
- East Pasadena192 mg/LVery hard
- Sierra Madre161 mg/LHard
- South Pasadena128 mg/LHard
- East San Gabriel192 mg/LVery hard
- Glendale86 mg/LModerately hard
- La Crescenta-Montrose3 mg/LSoft
- Arcadia54 mg/LSoft
Hardness data: TapWaterData US Water Hardness (utility report, October 14, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.