Originally posted by jschmid
But I don't think the high-pressure water will hurt anything as long as you don't do anything weird with it. 
"if your car is completely crapped over with dirt, dust, and salt ... the particles act as a sandpaper when the high-pressure water hits it. it's like your sandblasting your finish."
i've heard that one before ... sounds like it could be true, but i haven't tried it.