Hard water in the Gallatin Valley: city water, wells and Big Sky

The white haze a sprinkler leaves on a window is mineral: calcium and magnesium carried in the water and left behind when it dries. How much there is depends on where your water comes from, and in this valley that varies a lot.

How hard is the water?

The state’s assessment adds two details. The city’s smaller Lyman Creek source is harder than its creek water, and during spring runoff the creek water softens, to “soft or moderately hard.”

Why softer water still spots glass

Andersen puts it simply: even soft water leaves spots when it dries on a window. The glass industry’s standard for spot-free rinse water is 20 parts per million of dissolved solids or less, and it says ordinary tap water is not acceptable for that job. Ordinary tap and well water here is well above that, so a sprinkler that hits glass leaves something behind every time. Harder water just leaves more, faster.

Spots versus damage

Fresh deposits sit on the surface and come off with the right product and patience. The glass industry warns against letting water and residue sit on glass, and says glass can be permanently damaged if it is cleaned too rarely or the wrong way. Vitro, a major glass maker, notes that glass which is properly cleaned and dried resists that kind of damage.

Nobody authoritative publishes a timeline for how long sprinkler spots take to damage a window, and we will not invent one. The practical answer is the same either way: stop new spots, and deal with the old ones sooner rather than later.

What to do

1. Turn the sprinkler head so it misses the glass. It costs nothing and it is most of the fix.
2. Remove the spots already there, gently. How to remove hard-water spots without scratching the glass.
3. If a pane still looks cloudy once it is clean and dry, the glass itself may be damaged. That is a replacement, not a cleaning.