I am not sure where the obsession with drinking started. Maybe Gatorade (Pepsico) had something to do with it? Maybe it originated in California or the Southwest, home to many endurance racers, and areas where dehydration can be a real life threat. Maybe the bottled water companies had something to do with it? Whatever its origin, it has gotten out of control in more ways than one. One indication is how it has entered everyday life. This is clearly illustrated by people walking around in cities carrying water bottles. It can also be seen in "health trends" that advise you to drink a gallon of water everyday. Or triathletes carrying enough water to cross the Kalahari in the bike leg of a sprint triathlon that takes less than an hour to complete.
Clearly too many people stand to gain monetarily from this craze so a reversal will be difficult to achieve.
Dehydration is also blamed for loss of performance. We are told that as little as 10% dehydration can cause an enormous -some say 50%- loss of performance. That has many racers worried. The truth however is a bit more complex. On the one hand we have various individuals tested to exhaustion on various devices, where results show that people get tired and dehydrated when exercising for long periods of time. Many of these people also develop cramps. Both correlations are often misinterpreted as causal mechanisms.
On the other hand, we have record-setting performances by well-trained athletes, who are often very dehydrated when they finish the race. Occasionally we see people collapse and guess what, when you check their hydration levels, you find they are quite dehydrated. These people too, often develop cramps.
Then there is the magic moment, when someone develops a cramp and stops to drink and swallow a few salt tablets. And guess what? The cramping goes away. The question is, why? The answer is rather simple: they slow down or rest for a while.
Scientific studies have shown that cramping has nothing to do with hydration levels, but is instead related to inadequate training. The best remedy is to stop what you are doing. Even a short break will do wonders here. If you want to avoid cramping, you need to train better. And better means you need to mimic the race situation both in intensity and length.
The less well trained you are, the faster you will dehydrate and the more of an effect the dehydration will have on your performance. When you are poorly trained, drinking more will have little effect on your performance, although it may correct your dehydration. If things go really poorly, you may over-hydrate and end up in the hospital.
I will discuss this in more detail later, but for now it should suffice to say, that you should be able to run or bike for an hour in average ambient temperatures without having to drink at all. There should be no effect on your results. If anything, the loss of water should enhance your performance, as you will now be lighter. But don't extrapolate to longer events. Here you certainly do need to drink something.