I bring water almost all the time unless I'm doing something fairly short. I think I'd be OK without it for anything under an hour, but I like to have it anyway. I like to time my drinking with the locations of the water stops for my upcoming race. I figure, if I'm training for a race where I'm definitely going to be taking fluids, I might as well be taking in fluids during my training, and in roughly the same intervals, so I that my body is used to it.

FWIW, I use a Camelbak Quick Grip water bottle. Don't know if there are better options but it keeps my water pretty cool without making my hand cold.

I will say that it's easier to run without a bottle. I hadn't noticed it being harder when running with the bottle, but when I did some short runs in my taper before my last race, I ran without the bottle (since I wouldn't be carrying it in the race) and noticed it was a bit easier and more efficient without it.

I bring water if I am running over 20 miles and it is really hot (this never happens, as I only do spring marathons so most of my long runs happen in the winter).

Rarely do I ever take water. Only if it's very hot and humid and I'm doing 18 or more. I routinely do long runs of 18+ miles with no water or fuel. The body is designed to handle this. It's more about personal preference than anything else.

Why not try it out - bring some water with you but don't drink it unless you feel thirsty. After a few times you'll get a sense of whether it's worth carrying or not!

Another thing I do is to bring the water bottle but only part-fill it. I'm never going to drink the whole thing, so I don't see why I'd bother carrying it either.

When I'm running about 5-6 miles or less, I just travel without liquids. On longer runs, I tend to plan my route so I can keep on coming back to my starting point and grabbing a quick drink of water or sports drink (tend to stash it in the back of my vehicle) every few miles.

I do tend to train early in the morning before it gets too warm too.

I pre-hydrate, so I rarely carry water for training. I may carry a small bottle on distances over 10 miles, but that has varied depending on where I run (if there are water fountains) and the weather. I run in a humid and hot location (Texas), so the summers are my only real problem with hydration.

During longer races (10k or half-marathons are the only "long" races I've done), I'll get some water or sports drink at some of the stops, depending on how I feel.

Water over 2 hours, gel flask over 2.5 hours.

I tend to have rather low blood pressure and in hot and humid Florida if I haven't had any fluids in a 8 mile run I am pretty lightheaded when running and even more so when I stop. So I have been drinking if running for more than an hour to avoid that. I don't always carry fluids- sometimes I run loops and drink at the starting point.
-

I have been wondering this myself lately. I currently run around a lake (about 10mins around/lap) so I can get back to my car, where my water is stored, if necessary. I have thought about a hydration belt so that I am not tied to the lake, but I am also allergic to bee/wasp stings, and need to have an epi pen available as well. I haven't bought anything yet as I can't find a hydration belt with a pocket big enough to carry my epi pen.... /sigh. The search goes on.

This depends somewhat on weather for me but anything over 6 miles and I'm definitely bringing water. If it's summer I bring it period.

I have one of those handheld bottles and I bring it for anything over ~6 miles. They're really pretty handy once you get used to them. I also like to bring a Gu for a 9+ mile run, and they've got a little pocket to stick that in.

For road runs, I carry nothing for anything under 10 miles, a handheld for 10-20 miles and a Camelbak for anything over 20; For trails, I take my hand held for all runs under 15 and my Camelbak for anything over 15...