I do 6k to 10k on my runs 4 days a week and never REALLY need water... Even on hot days, I'll just make a quick detour to a fountain. Just listen to your body and it should be fairly safe.
I just rest personally, and reset the count.
Here's a question for the thread: what do you guys do about water on a run?
My usual run is 8km (although I sometimes do 10km on weekends), less than an hour, and I don't take any water with me. I'll have a small glass before I go and that's that. Other running friend says this is A Real Bad Idea. I could chug a pint glass before I go but I really don't want to lug water with me, do I have to? I only occasionally feel thirsty. I sweat like a fountain though so I probably should. Or is it ok to just pre- and post-chug for 40-50 min runs?
To help deal with hydration, I usually drink a good amount of water (2 pints?) an hour or two before my run. Make sure to pee before your run or you'll be sorry.