Just an extra point to keep in mind, long duration athletes should be having 15Ml of water per kilo per hour. Ie. I'm 70Kg and if I were to go on a 3hr bike ride it would be 70 x 15 x 3 = 3150Ml or 3.1L
Somewhere I've also got a really good assignment on energy systems (18/20), I'll have a poke...