Spray, but the cloths just get wet far to fast for my liking, and to be honest the windows I got the kit for are really filthy and it just cant clean them. I think it would be fine if it was just for taking dust of the glass but not much more than that.
maybe using to much on the glass, i use 1 pad per 6ft x 6ft glass and at the end ot that i could do half again, and its just slightly damp to touch, you dont need much liquid on the glas as the pad dose the hard work.
i yet to use pure water to clean with, i used this in my bottle,
http://www.toolstation.com/shop/Cleaning+Pest+Control/Window+Cleaning/Glass+Cleaner+1Ltr/d260/sd3231/p85116