How Much to Drink When Running?

The amount people drink varies greatly between individuals. I sweat a ton and can lose more than 5 pounds on a long run, yet I rarely ever drink on training runs of less than 14 miles. One thing I have noticed is when I do my longer runs of 14+ miles and I drink, the more I drink the more I want, and this doesn't start until after I start drinking. If I start at say 4 miles, then I'm wanting more in another mile or so, whereas I don't normally drink and don't want anything at any point in a run of less than 14 miles. It's like once the body knows it can get something it constantly wants more, but if it knows nothing is coming then it makes adaptations. No doubt there is a point at which the adaptation stops and then a need must be satisfied. Cold or heat doesn't seem to affect my hydration for training runs.

From the official "position stand" of the American College of Sports Medicine:

"Although the impact of fluid deficits on cardiovascular function and thermoregulation is evident, the extent to which exercise performance is altered by fluid replacement remains unclear. Although some data indicate that drinking improves the ability to perform short duration athletic events (1 h) in moderate climates (7), other data suggest that this may not be the case (40). It is likely that the effect of fluid replacement on performance may be most noticeable during exercise of duration greater than 1 h and/or at extreme ambient environments."

This is in line with the general party line in sports medicine (at least what's readily accessible to the public)--aim to replace water lost during exercise (to the extent possible...which is not 100%), but particularly after 1 hr of exercise, when you should generally consume fluids containing electrolytes rather than just water.  (In other words, water--or no hydration--is fine during the first hour of exercise, assuming you've properly hydrated before starting.)

This pretty much is in line with my approach.  I rarely take hydration with me for workouts of less than 90 mins., except in temperatures of around 90F or above.  When I do take hydration, I tend to take 4-6 oz of sports drink every 20-30 mins., again depending on temperature.  That's on the low side, but I've never had any issues with dehydration, even though I do a lot of running in very hot temps.