A meaningful split between Twin Cities surface-water sources (Mississippi River for Minneapolis, glacial-lake reservoirs for Saint Paul, 70-120 mg/L) and the outer-ring suburban groundwater pulled from the Prairie du Chien-Jordan aquifer (140-200 mg/L). The hardness difference between adjacent municipalities can be substantial. Lake-country sources vary widely, generally moderate.
HOW IT BREAKS DOWNmoderate (Minneapolis, Saint Paul, inner suburbs), hard (outer-ring groundwater suburbs)
A Minneapolis customer and a Bloomington customer ten miles apart can have meaningfully different lower-sash mineral residue problems. Deionized final rinse is essentially mandatory on the groundwater-suburb routes and is best practice on the Twin Cities tap-supplied routes as well. The seasonal variation in Mississippi-source hardness — softer in spring snowmelt, harder in late-summer low flow — is real enough that the protocol on year-round commercial accounts needs to adjust.
Minnesota spans 4 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.
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 Minnesota the spread runs from Duluth at 50 mg/L to Brooklyn Park at 180 — a difference big enough that the same bottle of cleaner behaves differently in each.
This page is about Minnesota's water and nothing else. For how cleaning actually works in Minnesota across the year — climate, seasonal timing, the local contaminants, the housing stock — see the Minnesota 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.