It can EASILY warp the rotors when you do that. Don't believe me? Try it. Get up to 80mph and slam the brakes in the rain. Then when you brake next time, you'll feel the difference.

 

This is only an issue at race track temperatures. Street temps are not an issue, unless of course you just finished bedding in some pads, but if that's the case you already know the what to's and what not's of brakes.

Spraying cold water on a hot rotor probably isn't the best idea, but for all general purposes it won't do anything but fizzle. It's the extreme side of it that will cause problems like taking a glowing hot rotor and submerging it, COMPLETELY, in cold water. In that case you might have a problem...the problem being that you just drove your race car into a frozen lake.

 

Then explain why I ran on a track for over an hour IN THE RAIN and had zero brake problems. And no, I don't believe you.

 

I used to washed my wheels, after a few time of cleaning it. I got sick of it. It was a b!tch to wash the wheels. That's why I bought some dark rims It looks good that way.