FYI - I used to use coin-ops - I'd bring a mit, and pretty much use them for their space as well as to get soapy water on the car and rinse it off. I rinsed my mitt with the wand, but only the mitt touched the car.
TWO WARNINGS
1. The pressure is high enough to cause serious injury - I sprayed the mitt on my hand and managed to spray the inside of my wrist - it broke the skin. Hurt like crazy. I was LUCKY - you can get serious infections this way because this stuff can penetrate DEEP.
2. Although I USUALLY had good luck, you must know that this water is "recycled". You have no idea how often they clean their filters, and you have no idea what stuff people have washed off their cars prior to your using that water. Could be parts cleaner, battery acid, god knows what. Anyway - even though I pulled the car out and went to dry immediately, I got some
horrendous water spots once, and I attribute it to some bad, bad, bad stuff in their water.
Do you know anyone in the area with a house? Would they let you use their hose? I think this is infinitely preferable.