There are many people already doing this. Most as you said use a water rinse with some high polymer additive then dry with chamois. No need to agitate this way. Also the cars are so close together you can not use a pole of any size to get to the vehicles. I have introduced 2 of the local companies in my area to pure water and now they are no longer drying the cars just rinsing with pure water and air dry. Pure water is so aggressive there is no need to agitate. Also because the cars are done weekly they clean up nice. The biggest challenge is the large amount of pure water needed to wash 200 cars. Most of these companies are using a 2-3 gallons per minute PW and drawing from a 300 gallon tank. You will go through the tank before you finish all the cars on some lots that are big. Most of these companies that are doing this full time doing 2 or 3 lots a day are using the systems like IPC Eagle Hydrostation that can produce up to 8 gpm of pure water so the tank can fill fast. Do you have a way to set up a tank based system and bring the pure water with you? We have a roof cleaning system that could be used to rinse the cars. You would need a large tank that you can buy locally.