San Diego hard water: about 14 grains per gallon
San Diego tap water is very hard: about 14 grains per gallon (237 to 243 ppm) on average. Those numbers come from the City of San Diego's 2025 drinking water quality report (PDF, opens in new tab).
San Diego water hardness
Grains per gallon, from the City of San Diego 2025 water quality report. Sacramento river water shown for comparison.
Where does San Diego water come from?
The city's report says San Diego imports most of its water. Most of that is untreated water bought from the San Diego County Water Authority. It is a blend of Colorado River water and State Water Project water from Northern California. The city also stores water in local reservoirs.
The city treats this water at three plants: Alvarado, Miramar and Otay. All three averaged about 14 grains per gallon in 2025. A small share is treated water the city buys from other plants, and that averaged about 8.5 grains per gallon.
What 14 grains per gallon means at home
- Heavy white scale on faucets, shower heads and tile
- Cloudy, spotted glassware
- Scale inside tankless and tank water heaters
- Soap scum that keeps coming back
Do you need a water softener in San Diego?
For most homes, yes. At about 14 grains per gallon, the water is very hard everywhere the city's plants serve. A softener cuts scale, saves on cleaning and helps water heaters last. Get your tap tested so the system is the right size.
See what a softener costs, or read reverse osmosis vs. a water softener to see which does what.
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Is San Diego water hard?
Yes. The City of San Diego's 2025 report lists average total hardness of 237 ppm at Alvarado, 242 ppm at Miramar and 243 ppm at Otay. That is 13.8 to 14.2 grains per gallon, which is very hard.
Why is San Diego water so hard?
The city imports most of its water. The report says most of it is a blend of Colorado River water and State Water Project water. Colorado River water picks up a lot of calcium and magnesium on its way to Southern California.
Which treatment plant serves my home?
The city's report has a service area map for the Alvarado, Miramar and Otay plants. Some areas overlap, so your water can come from more than one plant. A tap test gives you your exact number.
Keep reading
DataWater hardness by cityHow hard the tap water is in US cities, from each utility report.
City dataLos Angeles water hardness: 6 to 14 grains per gallon6 to 13.8 grains per gallon by source. Hard.
GuideHow much does a water softener cost installed?Installed price ranges, running costs, and what drives the price.
GuideReverse osmosis vs. water softener: which one do you need?They do different jobs. Here is how to pick.