Water Hardness by City, San Diego to Temecula (2026)

Which areas have the hardest and softest water?

Most of San Diego County is very hard. The City of San Diego's three treatment plants average 237 to 243 mg/L (13.8 to 14.2 grains per gallon), Helix Water District, serving La Mesa and El Cajon, averages 206 mg/L (12.0 gpg), and Vallecitos, serving San Marcos, runs 242 to 255 mg/L.

The single hardest figure in the table is Lakeside Water District's own wells, at 472 mg/L (about 27.6 gpg), though most Lakeside homes get Helix-treated water instead. In the Temecula Valley, Rancho California Water District's imported water averages 230 mg/L and its wells 151 mg/L, so taps there get a blend of very hard and hard water.

In the Inland Empire most systems report hard water, by source from 63.14 mg/L (San Antonio Water Company) to 248 mg/L (City of Chino, city wells). The softest water we serve is on the LA Westside: LADWP and Santa Monica both report about 103 mg/L (6.0 gpg), moderately hard. The widest swing is Vista Irrigation District, from 54 to 310 mg/L depending on the source. Nothing in this table is a health concern; hardness is about scale.

Why does hardness change from year to year?

Most of the water in San Diego County is imported, and it comes from two places: the Colorado River and the State Water Project from Northern California. Colorado River water carries more dissolved minerals. The San Diego County Water Authority notes that the Metropolitan Water District's blend of the two shifts with how wet the year is and how Metropolitan runs its system. Local districts then add their own reservoir water, wells or desalinated water. A year heavier in Colorado River water tests harder at your tap.

One district's report shows the gap side by side. Eastern Municipal's water from the Mills plant, which treats State Water Project water and typically serves Menifee, averaged 5.1 grains per gallon. Its water from the Skinner plant, which treats a blend that includes Colorado River water, averaged 13.4. That's why every row in the table carries its report year.

What does hard water do to plumbing?

Hard water carries dissolved calcium and magnesium. When it is heated or evaporates, those minerals come out as scale. In a tank water heater the scale settles on the bottom, the burner heats through it, and you hear popping or rumbling. In a tankless unit it coats the heat exchanger, which is why tankless heaters on hard water need regular descaling.

The same minerals crust faucet aerators and shower heads, wear out fill valves and cartridges early, spot glass and leave film in the dishwasher. Hardness is an aesthetic and scale issue, not a health concern: there is no health-based limit for it, and every system in this table reports to the state on the standards that do apply.

How is a salt-free conditioner different from a softener?

A salt-based water softener is the only home system that removes hardness. It trades calcium and magnesium for sodium in a resin tank, regenerates with salt brine, and needs salt, a drain and power. After a softener, the water tests soft. See water softener installation.

A salt-free conditioner is a different product, and it is not a softener. It does not remove hardness minerals, so the water still tests hard and glass can still spot. What it is designed to do is reduce scale forming inside pipes and the water heater, with no salt, drain or power. It is the compliant option in the Inland Empire cities where new salt softeners are prohibited. See salt-free water conditioning and our water system guide.

How do you read your own water quality report?

1. Start with your water bill. The system named there is the one whose report applies to you, and it isn't always the one your city's name suggests.
2. Open the report. The Source link in each row goes straight to it. The State Water Resources Control Board also keeps every California system's filed reports on its electronic annual report site, which is where most of our links point.
3. Find the hardness line. It usually sits in the table of secondary or unregulated constituents, sometimes under a heading like “Sodium and Hardness.” Look for total hardness as calcium carbonate, printed in mg/L or ppm, which mean the same thing for drinking water.
4. Check what the number describes, and the year. One system average, one figure per treatment plant, and a range by source each tell you something different. If your system lists several plants or sources, your tap gets a blend the report doesn't pin down.
5. Convert it if you're comparing equipment. Softeners are rated in grains per gallon. Helix's 206 mg/L, for example, is the 12.0 grains per gallon printed in the same report.

How was this data collected?

Every figure is total hardness as calcium carbonate from the water system's most recent Consumer Confidence Report or annual water quality report, linked in the Source column. Where a city is served by more than one system, or one system reports its sources separately, each gets its own row. We print what the report prints: an average where it gives one, a range where that is all it gives. We do not average or estimate.

Grains per gallon are the report's own figure where it prints them. Otherwise they are mg/L divided by 17.1, rounded to one decimal, and marked with an asterisk. A few reports, including Eastern Municipal's and Otay's, print only grains per gallon; for those the mg/L is the conversion, also marked. Levels use the U.S. Geological Survey scale: 0 to 60 mg/L soft, 61 to 120 moderately hard, 121 to 180 hard, and above 180 very hard. A range that crosses two levels shows both.

No hardness figure was published for: City of Chino Hills, city wells (Chino Hills); Los Angeles County Waterworks District No. 29, Marina del Rey Water System (Marina del Rey). Those rows say “Not published” rather than show a guess.

Your own tap can differ from a district figure, because of the blend that week and your home's plumbing. If you are deciding on treatment, we test at your hose bib first.

What else do people ask about hard water?