Would it damage the disc brake on a car if I poured water on it after a long journey in the heat (and the discs were hot)?
Well, let’s see. Suppose you were driving on a long journey and it suddenly started to pour down rain. The brakes would get wet, wouldn’t they?
The discs are always hot, even after a short trip. Try touching one when you park the car after you get home from work or shopping. You’ll see.
I suppose under severe conditions you could warp the rotors, but other than that I can’t see how you’d cause any damage.
Why would you pour water on the brakes in the first place?
Heh, that’s true. I was just wondering. Thanks. I would assume that they would steam as well. I just have random car related thoughts sometimes 
no reason to do it and take a chance, rotors are $$$
OK children, now we are going to play a fun new game called “Warp The Rotors”…
Wow! Look at that steam! Isn’t that cool??
Exactly
While it is possible that one’s rotors might escape this experiment without being warped, I think that the probability of warping is high enough so that anyone contemplating this should rethink it.
What type of questions will we have next?
How about:
Will driving over nails and broken glass always result in tire punctures?
Will it really damage my engine if I go 20k miles between oil changes?
Does every interference engine self-destruct when a 10 year old timing belt snaps?
Hmmm…On second thought, we actually get that third question about once a week.
Oil change question is just about every other day. Timing belt questions happen on the days there’s no oil change questions 