Might work great if it stays cold enough but if there's any danger of snow/ice melting and refreezing don't try it... I did once and ended up with a tarp frozen to my car's windshield and doors, couldn't even get in to turn it on and get the heater going.
You just hold them a foot or two away from the window and move it a lot.
It's still not a great idea because it's going to take like 30 minutes to defrost your windshield, but in a situation where there's a frozen tarp locking you out of the car, it'll do
just don't use water. or do, but post the video.
yeah, at least in colder climates, it freezes way faster than you'd expect. Basically instantly, with a bad habit of pooling around the wipers
edit: turns out some people have also tried boiling hot water... I'd never have thought to try this, but, yeah, it'll crack your windshield.
some people will recommend rubbing alcohol blends, which work a little better, but they can dry out the rubber seals around the window. It's honestly better to just start the car 5 mins earlier than you need to use it, with the defrost on full blast, then come out and scrape it.
