The most varied water profile of any state — a patchwork of six major districts, each with its own source, treatment, and hardness profile, plus a meaningful population of Central Valley wells.
HOW IT BREAKS DOWNmoderate to hard (district-dependent)
California is not a single water market. The city of San Francisco drinks Hetch Hetchy water from the Sierra Nevada, which arrives at 70-90 mg/L — soft to moderate. The East Bay drinks Mokelumne River water from EBMUD, also moderate at around 70-100. The South Bay (Santa Clara Valley Water) blends imported State Water Project deliveries with local groundwater and runs harder at 200-280. Greater Los Angeles, served primarily by the Metropolitan Water District, drinks a blend of Colorado River, State Water Project, and local groundwater that runs 250-350 — hard, and the dominant southern California reading. LADWP, on a separate system serving the city of LA proper, blends MWD imports with Owens Valley aqueduct water and runs slightly softer at 180-260. The Central Valley wells, which are not on municipal supply, can run anywhere from 300 to over 450, with significant nitrate and arsenic issues in particular sub-basins. Cleaners working a route that crosses district boundaries need to know which water they are dealing with on each customer before they quote.
A blended system means hardness moves with the blend. Two addresses on the same utility can read differently, and the same address can read differently across a year, depending on which source is carrying the load that season.
California spans 5 hardness bands, which means there is no single answer for the whole state — the method changes as you move across it. Both ends are below.
Tap water is clean enough to be the last thing that touches the glass. Wash with it, rinse with it, squeegee it off, and nothing measurable is left behind when it dries. No distilled rinse, no deionized final pass, no spot-free rinse aid — the mineral load is too low to precipitate anything you would see. The failure mode at this end of the scale is not water chemistry, it is technique: streaks here come from a worn rubber, a dirty edge, or a pass that dried before it was pulled.
Tap water is still fine for most residential glass, with two exceptions worth knowing. Dark glass shows a faint mineral haze that lighter glass hides, and glass that is hot enough to flash the water off before you pull the squeegee will spot regardless of how soft the supply is. On both, a distilled final rinse costs about a dollar a window and removes the variable entirely. Everywhere else at this level, the water is not what is wrong.
This is the band where the water starts writing on the glass. Wash with tap — the surfactant holds the minerals in suspension while you work, so the wash pass is not the problem — then rinse with distilled and pull that. The rinse is the whole intervention: it replaces the mineral-bearing water sitting on the glass with water that has nothing in it to leave. This single change resolves most of the "I cleaned it and it still looks bad" complaints in this range, and it does not require buying a system.
A distilled rinse stops being an improvement and becomes the method. Tap water left to dry on glass at this concentration deposits a visible film within minutes, and the film is cumulative: each cleaning that ends in tap water adds a layer that the next cleaning has to get through first. Glass on a sprinkler line or under a runoff drip needs a maintenance interval, not just a better wash — the deposit is arriving faster than a cleaning schedule built around dust would predict.
The hardest water in North America — Phoenix, Las Vegas, West Texas, much of the limestone Midwest. At this concentration calcium carbonate precipitates out of any water that touches the glass and dries, so what you are looking at is essentially limestone, growing one molecular layer at a time. Tap water cannot be part of the final pass under any circumstance, including "just a quick rinse." Above roughly 300 mg/L, buying distilled by the gallon stops making economic sense against a DI filter or a pure-water pole system, and a residential owner cleaning their own glass twice a year is usually better served by a service that already owns one.
Hardest first — the order that matters, because the hard end is where the method has to change. Each figure is a service-area typical for the named utility. Within California the spread runs from San Francisco at 80 mg/L to San Diego at 290 — a difference big enough that the same bottle of cleaner behaves differently in each.
This page is about California's water and nothing else. For how cleaning actually works in California across the year — climate, seasonal timing, the local contaminants, the housing stock — see the California cleaning guide.
For a figure at your own address rather than your city, the Hard Water Scorer takes a ZIP code. If you run a pure-water system, the TDS diagnostic reads the other end of the same problem.
USGS national hardness survey data and utility Consumer Confidence Reports, 2023 vintage. City figures are service-area typicals for the named utility, not readings from any one tap. State ranges are the lowest and highest typical municipal values across the state, so they bracket the populated area rather than describing an average resident. Where a state blends sources seasonally, the range is wider than any single address will ever see.
Private wells are outside all of it. A well is whatever the rock under it says, and the only number that describes one is a test of that tap. Have a reading that disagrees with this table? Send it to us — a number that contradicts the table is worth more than one that confirms it.