We've had a draught problem here in Ga also with restrictions varying depending on the seriousness of the draught. There are a number of hand wash car washes in the area that are exempt since they recycle their water. That's an alternative when they really get grungy.
I just assumed it was a combined effort. You just have to be careful closing the door, hatch, hood, to make sure nothing gets caught, you know.
I have always understood that it is important to wash a car at least twice monthly to wash off atmospheric impurities in the air or natural dust from a garage that draws in the impurities when the car is driven or parked outside. I also heard that waxing a car is far less important than washing a car, although I do that at least a few times a year. I guess I find it therapeutic as well to wash the car and vacuum the interior. Since I transport my 100 lb puppy at least once a week for a ride to the woods or even running an errand, it seems like a good idea to have the inside cleaned as well. I am not associating showering, washing clothes or even cleaning the house to washing the car but I can't imagine not having a system or alternative to clean the car even in drought stricken areas. I know there were some dry cleaning methods that were popular years ago that resembled a large mop for the car's exterior where water was scarce.
Black Prius. Try to wipe off the excess spatter as it happens, wipe down the rear deck's water spots almost daily. Since our water actually is free (we have a mandated home well system for lawn care and the water district charges a minimum of $9 a month, which most people never exceed unless they have a pool -- you may now express your jealousy.......), I'll clean it up fairly frequently, twice or three times a week, usually with a bucket of water with a capful of Murphy Oil and a rubbing rinse, wipe down to dry. When I get serious, I spray the whole car, segment at a time, wipe it down, rinse as I go, dry with chamois. My microfiber towels leave a pattern on the Rain-Xed windows, I think, so I need to address that. I'm basically lazy, but I've never had a black car, so I'm trying to develop a good habit of keeping it clean. I also let God's car wash do what it can when it rains here (60 inches a year annual rainfall).
I'm a bit OCD when it comes to my car so I vacuum and wipe down the interior every week, wash the outside every other week, and wax it three or four times a year. When I was a teenager I had to drive my stepdads car and he was (and still is) a bit freekish about the upkeep of cars. In order to keep my driving privileges I had to keep the keep the car in pristine condition. I got lectures on fading paint, under-inflated tires, etc. Although I've become slightly less OCD, many of the habits have stuck with me. Every Saturday I'm out there checking the tire pressure and the oil and cleaning the car. I do go to a car wash bay to wash the car since they recycle the water, and if the car doesn't look dirty I'll go an extra week or two between washes. This car is a pretty big investment for me so I like to keep it nice
I switch off driving my Prius and my Tacoma, so the Prius don't get dirty a whole lot. I bought a cover for it and keep it covered when parked at my house. The birds are just terrible hitting my cars.