Sheesh, how much water do you need? I can do my trailer with less than 4 buckets soapy water then probably about the same amount worth of rinse with the hose sectiona at a time.
Water conservation was bred into me. We have NO city water at our house. We live by what falls from the sky only. No well either. Rainwater is channeled into a tank, about 30,000gal capacity, under the house. From there a shallow well type pump puts it into our own independent pressure system.
What keeps us thrifty is that 1000gal of water by truck costs well over $100.
Can't imagine dry cleaning a vehicle. Pushing the dirt around its surface cannot be good for it.