Hard water in Coronado, CA
Reported by San Diego, City of · 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 Coronado carries roughly 160 mg/L of dissolved calcium and magnesium, or 9.4 grains per gallon. That is hard water. The number comes from San Diego, City of, dated September 2025. Reports for this system disagree, with values from 160 to 206 mg/L.
At 160 mg/L, Coronado is 39 mg/L above the typical California figure of 121. Of the 10 nearest cities we track, 3 have softer water and 7 have harder. The range nearby runs from 128 mg/L in National City to 225 in San Diego.
What 160 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 160 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 × 9.4 gpg = 2,106 grains a day. A 24,000-grain unit regenerates about every 11 days.
EPA record for Coronado's water system
No health-based violations since 2016
Serves about 1,408,937 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 7
- Open now
- 0
TapWaterData ties Coronado to this system. EPA's service-area records do not name Coronado, 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 Coronado water hard?
Yes. It measures about 160 mg/L (9.4 grains per gallon), which the USGS classes as hard.
What is the water hardness in Coronado in grains per gallon?
About 9.4 gpg. One grain per gallon equals 17.1 mg/L, so 160 mg/L divided by 17.1 gives 9.4.
What size water softener do I need in Coronado?
For 3 people using 75 gallons each per day, 9.4 gpg works out to about 2,106 grains a day. A 24,000-grain softener covers that with a regeneration about every 11 days.
Has the Coronado water system had EPA violations?
EPA records show no health-based violations for San Diego, City of since 2016. There were also 7 monitoring or reporting violations, which are about late or missing tests and notices.
Nearby cities
- National City128 mg/LHard
- Imperial Beach200 mg/LVery hard
- Lemon Grove150 mg/LHard
- La Presa189 mg/LVery hard
- La Mesa150 mg/LHard
- Spring Valley189 mg/LVery hard
- San Diego225 mg/LVery hard
- Casa de Oro-Mount Helix212 mg/LVery hard
- El Cajon165 mg/LHard
- Rancho San Diego212 mg/LVery hard
Hardness data: TapWaterData US Water Hardness (utility report, September 27, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.