Old post but here goes my bit.
Read "Your body's many cries for water" if you are serious about knowing about hydration. One piece of information from it athletes need to know would be that used muscles hold a lot of water - so don't use them for a few days and you are going to take up more water when you do. He suggests water+salt for optimal hydration and then apparently you can't get into trouble by drinking too much - the potential problem being low brain sodium. I've told literally a couple of hundred people + about hydration and nutrition over the last nearly 20 years, and if there's one thing that comes back as making immediate difference it's water.
Also not all water is as hydrating as others. The more is in the water in terms of general minerals, the harder it is to hydrate from it. So most tap water is very slow.
Also if you're into nutrition info - take a look at http://www.westonaprice.org - I don't take standard sports nutrition at face value. This is info from exceptionally healthy and strong races of the early 20th C. The isolated Swiss sent their athletes out to walk over the national competitions..... with raw cream to sustain them.
And another also .... information is coming out that fructose when quickly taken up as it is in energy gels and fruit juice is not at all good for health for one thing - and glucose would be much better and does not destabilise blood sugar as much (sucrose is 50/50 of each). Take a look at sugar the bitter truth on you tube.