"Magically Appearing" Hard Water Stains

Hey guys, new to the site, love all the info I’ve found reading through. I have a strange situation. Cleaned a customer’s home about 2 weeks ago using traditional methods and a dawn solution. Everything went well and customers were very pleased. I got a call a couple days ago from them saying that after a storm (with sideways rain) that the windows on the lake side of the home (which the rain battered) now had spots all over them which has never happened before. I went to take a look and sure enough, the windows all had hard water stains on them. Funny thing is, the windows weren’t stained when we cleaned them (other than a few minor stains) and she says that no hose/sprinkler etc has been used around them. What could have caused this? And what is my best option of removing the stains? I was thinking about using a vinegar solution with non-scratch pad and then wfp them clean. What do you think???

If it’s truly hardwater staining, a WFP will likely dissolve the light stains. Rain does not contain hard water elements, so despite them claiming no one hosed the windows, it’s just not possible for rain to leave hard water spots.

It would not surprise me that someone (kid) sprayed the windows or someone hosed them after the storm because they got pretty dirty from wind and rain, then realized the mistake they made.

Pure water is some pretty amazing stuff, so long as the stuff doesn’t bake on the glass in hot sun for an extended period of time.

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I could easily see they maybe attempted 2 remove spider webs from the siding framed or eaves, even gutters being Lakeside.

That doesn’t happen from Rainwater

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Rain water will not cause the spots. But it can carry some stuff if it runs off the side of the house. I see it sometimes where the window frame is badly oxidized, there are visible “currents” where the rain water has dragged particles down to stain the glass.

That scenario doesn’t happen overnight though. If there were no spots just a short time before, then it seems likely some yahoo soaked 'em and let the hard water bake in sunlight.


Thanks for the input guys. Going to head over tomorrow, hit it with the WFP and see what happens.

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You said you washed it with a dawn solution? Perhaps you used a little too much dawn, and the dawn remained on the panes, and when the storm happened and the water hit them just right, the water marks could be soap bubbles?

Try just washing them with water, or wiping them and see what happens?

Are you sure they are hard water spots and not just dirt spots from the rainstorm. Sideways wind can throw some dirt around.


Went today to handle the issue. WFP took care of the problem although homeowner freaked when he saw me “soaking down all the windows!” and started toweling them off. I guess he must’ve missed the conversation I had with him when I arrived about pure water and making sure his pressure washing guy didn’t let the tap water dry on the glass and create HW stains in the first place. Oh well. A little extra work to please a customer but in this particular tight knit community, one bad reference can have a ripple effect. Thanks for all the help!


I’m guessing then that if they came right of with wfp they weren’t hard water stains, just dirt.

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Yep, anything can be sticky. A little or a lot. The problem is it is difficult to educate our customers. They are often amazed by the very simple things. Like a rubber blade removing the water from the glass. I had one guy ask me where all the water went. So I told him, ‘I squeegee it off the glass, it goes on the sill, it evaporates and goes into the air, and then YOU breath it’. He didn’t like that. These days I am more tactful.