When it gets hot here in Texas, I use a Rocket Camelbak on my road bike. http://www.amazon.com/o/ASIN/B0009H8...apstrikeco-20/

Unfortunately it's no longer made. I like it because its light and is fairly aerodynamic. You will drink more, which is good, but may run out of water before you realize it. I carry an insulated water bottle as a reserve and for external cooling.

For those who may not know, myself included until a few weeks ago, the Camelbak was invented in 1988 at the Hottern 'n' Hell Hundred here in Texas.

http://www.camelbak.com/en/Sports-Re...Our-Story.aspx