I wouldn't do it dry. I live in a flat too, it's really not that big a pain to fill a big bucket of water in the bath, using the shower head to get the car shampoo nice and bubbley, and then carry it down to the car. Then do it again with clean water for the rinse.
I'm FAR from a hardcore car washer, I shampoo, rinse, dry, then coat in Mer (available at Halfrauds) and polish off, before applying bumper care to the black vinyl. Mer also goes on the alloys and makes it easy to wash dirt off the next time around.
Speak softly and carry a big stick.