I use the sheeting method myself and it works great. I usually wash in the evening on weekend after being home for the entire afternoon.
I use the Mr. Clean Automotive Car Wash Kit to wash my car but mostly for the spray nozzle. However, if I have to wash in the afternoon or before a wax, I'll use the water filter feature in the kit. It runs the water through a filter like a Brita filter getting rid of the mineral deposits. So you're really spraying down your car with filtered water. I'll dry afterwards anyway but this way if I miss a spot, it won't turn into a hard water spot.
I bought mine from Canadian Tire and I think it was around $30? I still prefer to use a bucket for the soap since it gets the dirt of easier than filling the spray nozzle with the soap and trying to spray the soap on.