Cucamonga Valley Water District's 2025 report puts Rancho Cucamonga at 125.5 mg/L, with samples from 109 to 142 mg/L, which is hard and only just: the average is barely over the USGS line for hard and some samples fall below it. The supply was 51 percent groundwater from the Cucamonga and Chino basins, 41 percent imported State Water Project water and 8 percent local canyon and tunnel water, and the district disinfects with chlorine. Rancho Cucamonga is one of seven cities under a regional ordinance from the Inland Empire Utilities Agency, and Fontana, Ontario and Upland have their own suppliers.
Hard, and only just
Cucamonga Valley Water District's 2025 report puts the average at 125.5 mg/L, which calculates to about 7.3 gpg. The samples run from 109 to 142 mg/L. USGS calls water hard from 121 mg/L, so the average is barely over that line and a few samples fall a notch below it. Very hard starts above 180, and nothing in the report comes close. Next to San Bernardino, the other San Bernardino County city on our table, it is much softer. The full scale is on the hard water by city page.
What that means in practice: hardness here sits in the hard band, and what you can taste is a separate question. The district disinfects with chlorine, and its report lists a free chlorine residual of 0.53 ppm on average. That is why this page starts with drinking water.
Where the water comes from
The district's 2025 report gives three sources. Groundwater from the Cucamonga and Chino basins was 51 percent of what it delivered. Imported State Water Project water, treated at the district's Lloyd W. Michael plant, was 41 percent. The other 8 percent came from local canyons and tunnels in the San Gabriel Mountains, including Cucamonga, Deer, Day and East Etiwanda canyons.
Who else supplies the area
State water-system boundary data suggests ZIP codes 91701 and 91730 are almost entirely Cucamonga Valley Water District and 91737 mostly so. The north and Etiwanda ZIP, 91739, is only partly mapped to the district, and a slice of Ontario's 91764 falls inside it. Neighbors Fontana, Ontario and Upland each have their own supplier, Fontana Water Company, Ontario's municipal utility and the City of Upland, with their own reports. Check your bill before you rely on this page's number.
Rancho Cucamonga's rule on water-conditioning equipment
Rancho Cucamonga is one of seven cities, with Chino, Chino Hills, Fontana, Montclair, Ontario and Upland, under a regional ordinance from the Inland Empire Utilities Agency (section 2.6). It limits new and replacement water-conditioning equipment that discharges to the sewer. Equipment already installed can stay. Cucamonga Valley Water District restates the rule on its own site. What Nuvia recommends in Rancho Cucamonga has to fit within it, which is why this page starts with systems that send no salt down the drain.
What we lead with in Rancho Cucamonga
Start with the water you drink. Reverse osmosis drinking water puts a membrane at the kitchen tap, where dissolved minerals and the taste of chlorine both get held back. For every tap, these are the whole-house options:
- Nuvia Sentry is a three-stage whole-house system with a carbon block filter for chlorine taste and odor and a scale-inhibiting media, with no salt or chemical additives.
- Nuvia Advantage is a five-stage whole-home filtration system with carbon filtration for chlorine and odors, without salt or added chemicals.
- Nuvia Scale Shield is designed to reduce and inhibit scale from calcium and magnesium in plumbing, appliances and fixtures.
See salt-free water conditioners for how the options work.
Start from your own tap
At 7.3, your own tap tells you more than a city average does. The free water analysis shows it to you before you spend anything on a system.
Nearby cities
Sources
- Cucamonga Valley Water District Water Quality Report (2025 water data, posted 2026)
- Cucamonga Valley Water District, page on equipment that discharges to the sewer
- Inland Empire Utilities Agency, rebate program page naming the seven regional-ordinance cities
- Fontana Water Company Consumer Confidence Report (2025)
- Ontario Municipal Utilities Consumer Confidence Report (2025)
- City of Upland Consumer Confidence Report (2025)
- USGS Water Science School: Hardness of water
Questions people ask
How hard is the water in Rancho Cucamonga?
Cucamonga Valley Water District's report gives an average of 125.5 mg/L, calculated to about 7.3 gpg, with samples from 109 to 142 mg/L. USGS calls water hard from 121 mg/L and very hard above 180, so this is hard, only just, and some samples fall a notch below.
Where does Rancho Cucamonga's water come from?
The district's 2025 report gives three sources: 51 percent groundwater from the Cucamonga and Chino basins, 41 percent imported State Water Project water treated at its Lloyd W. Michael plant, and 8 percent from local canyons and tunnels in the San Gabriel Mountains.
Is all of Rancho Cucamonga on the same water district?
Nearly all of it, but not every edge. State water-system boundary data suggests the north and Etiwanda ZIP, 91739, is only partly Cucamonga Valley Water District. Your water bill names your supplier.
Why does this page only talk about filtration, reverse osmosis and salt-free systems?
Because of a regional rule. Rancho Cucamonga is one of seven cities under an Inland Empire Utilities Agency ordinance that limits new and replacement water-conditioning equipment that discharges to the sewer. Equipment already installed can stay. We start with systems that send no salt down the drain.
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