I purchased two 32 oz. Nalgene bottles. Having two bottles means always having cold water ready and available. I also bought a splash guard for these wide-mouth bottles so that I can drink from them while being active without spilling on myself. Finishing two bottles seems like less than drinking 8 glasses of water, but it's the same amount! Also better for the environment than plastic bottled water!
I purchased my Nalgene bottles and splash guards at Amazon.com.