Pomona Water Is Very Hard — Here's What It Costs You Each Year

Why Is Pomona Water So Hard?

Pomona’s water comes in at 14.4 GPG (246 ppm), which puts it squarely in the “very hard” category. That’s roughly double the US national average of about 7.3 GPG, according to USGS data. But here’s the thing about Pomona: the city doesn’t rely on a single source. Like much of Southern California, Pomona pulls from a blend of local groundwater and imported surface water, and both paths lead to the same destination — dissolved minerals.

The local side of the equation is classic California basin geology. Pomona sits in the Pomona Valley, part of the larger Upper Santa Ana River watershed. The valley floor is layered with alluvial deposits — gravel, sand, and silt washed down from the San Gabriel Mountains over millennia. Rain and snowmelt from those mountains percolate into the ground and move through this alluvium, but the water also spends time in older sedimentary formations that are rich in marine deposits. Those ancient sea beds are loaded with calcium carbonate and magnesium compounds. As groundwater moves through them, it dissolves those minerals the way hot water dissolves sugar. By the time it reaches a well, the water has picked up a heavy mineral load.

The imported surface water doesn’t escape the hardness problem either. A large share of Southern California’s supply comes from the State Water Project, which delivers Sacramento–San Joaquin Delta water down the California Aqueduct. That water travels hundreds of miles through the San Joaquin Valley, where it picks up dissolved minerals from agricultural runoff and the valley’s alkaline soils. It’s not as hard as the local groundwater, but when it’s blended into the distribution system, it still pushes the final number up. The result is a supply that sits well above the 10.5 GPG threshold USGS uses to define “very hard” water.

You’re not imagining it if your showerheads clog faster here than they did somewhere else. At 14.4 GPG, scale builds quickly on heating elements, inside pipes, and on fixtures. The EPA doesn’t regulate hardness as a health hazard — it’s purely an aesthetic and nuisance issue under their Secondary Maximum Contaminant Level rules. But nuisance is a strong word for what scale does to your water heater and your detergent budget.

How Pomona Compares to Nearby Cities

Pomona’s hardness is typical for the inland valleys of Southern California, and it’s broadly in line with what your neighbors deal with. The cities immediately around Pomona — Claremont, La Verne, San Dimas, Diamond Bar, Walnut, Chino, and Ontario — all sit in the same general geologic setting. They draw from the same kinds of alluvial aquifers and the same imported State Water Project supplies. That doesn’t mean every city reads exactly 14.4 GPG, because local well fields and blend ratios differ. But the underlying geology doesn’t change much across the valley floor, so the water in those cities runs in the same very hard range.

If you’ve lived in Claremont or La Verne and noticed the same white crust on your faucets, you’re not imagining it. Those cities sit closer to the foothills, where the alluvial fans are younger and coarser, but the mineral content of the groundwater is still substantial. Head south and east toward Chino and Ontario, and you’re moving into the same basin with the same marine sediment influence. The water there is comparably hard.

The contrast gets sharper if you drive toward the coast. Cities like Long Beach or Santa Monica pull from different sources and different treatment blends, and their water generally runs softer. But that’s not the comparison that matters for you. Within the Pomona Valley, hard water is the norm, not the exception. If you’re moving here from a soft-water city in the Pacific Northwest or New England, the difference will be obvious within the first week. If you’re coming from elsewhere in the Inland Empire, Pomona’s water will feel familiar.

The practical side of that hardness is where the costs show up. According to the Water Quality Association, hard water raises energy, appliance-wear, and cleaning costs — an industry estimate that scales with your actual hardness level. Battelle Memorial Institute and the WQRF found that gas water heaters lose roughly 4% efficiency per 5 GPG of hardness in a typical 50-gallon-per-day household. At 14.4 GPG, that’s a meaningful hit to your energy bill before you even factor in the scale buildup. The DOE notes that just a quarter-inch of scale can cut water-heater efficiency by up to 40%. And hard water shortens water-heater service life by an estimated 30-50%. The cleaning side is just as tangible: WQA and Battelle research from 2010 showed you can use up to 50% less laundry detergent and up to 70% less dish soap when you’re working with soft water instead of hard. That’s money back in your pocket every single month.

How does Pomona stack up against the rest of California? It's very hard at 14.4 GPG — Oxnard, Berkeley, and Ventura sit nearby with different numbers. See the full hardest-water ranking for context.

See where Pomona sits on the California water hardness map →

Want the broader explainer on what hardness actually is and how it behaves? Read hard water vs. soft water, explained.