St. Louis softens its river water at the plant, yet the 2025 average still lands in the hard range. Here is what that means for glass, chrome and tile, and how to keep up with it.
People who move to St. Louis are often surprised that a city on two great rivers has spotty shower doors. The water is treated and softened before it reaches the tap, but the minerals are not all gone, and what is left shows up wherever water dries.
This guide explains where city water comes from, what the hardness numbers mean, which surfaces show it first and the cleaning habits that keep mineral film from becoming permanent.
The City of St. Louis Water Division runs two treatment plants. Howard Bend draws from the Missouri River. Chain of Rocks sits on the Mississippi just below the confluence, but the water reaching its intakes is still mostly Missouri River water. Like most river water, it carries dissolved calcium and magnesium.
The Division treats it with precipitative softening, a process that removes part of that hardness at the plant. Its 2025 report lists an average pH of 9.52 and average total dissolved solids of 298 parts per million.
The 2025 report puts total hardness at an average of 129 parts per million as calcium carbonate, with a range of 80 to 206. The U.S. Geological Survey classifies 121 to 180 milligrams per liter as hard, and parts per million and milligrams per liter are the same thing for water. So on an average day city water sits near the bottom of the hard band, and on some days it is softer or harder than that.
The practical result is mineral film that builds slowly but steadily. It is less dramatic than in very hard water cities, which is why it is easy to ignore until it has etched glass or crusted a faucet base.
Anywhere water dries in place collects minerals. In St. Louis homes, those spots are predictable.
Squeegee or towel off shower glass after each use; water that never dries on the glass leaves no minerals behind. Wipe faucet bases with a dry cloth when you finish at the sink. For buildup that is already there, a mild acidic cleaner made for mineral deposits works on glass and chrome, used as the label says and rinsed well.
Be careful with acids on natural stone, old marble and some older porcelain, which can etch. Many city bathrooms are close to a century old, since about 58 percent of homes date to 1939 or earlier, so test on a hidden spot first. A One-Time Deep Clean treats shower glass for hard water spots and details faucets, and a bi-weekly Recurring House Clean keeps it from building back.
Hardness is about cleaning, not safety, but one water question in older homes is about safety. The Water Division keeps a public inventory of lead service lines and advises flushing the cold tap for 5 minutes before drinking or cooking when water has sat for several hours. Look up your address in the inventory if your home is older, and use cold water for anything you drink or cook with.
Not every part of the metro drinks city water. The City of Florissant lists Missouri-American Water as its water utility, so Florissant homes should look at that utility's own report for their hardness number. The habits above work the same way whatever the source.
The questions St. Louis homeowners ask most often about this topic, answered plainly.
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