I carry a Hydrapak slung on back which can hold up to 1/2 gallon of water. As I pedal along, I can sip the contents through a tube without needing to stop. To keep the water cold for a while, I can drop a few ice cubes into the Hydrapak unit before starting out. I use the hydrapak unit for medium to long rides or ones that involve me riding in extra hilly or mountainous country.
I also carry a plastic 32OZ. water bottle in a cage attached to the frame. This is handy on short rides or can be used as a back-up to refill the hydrapak unit. If it's hot out, it's good to dump the contents over your head.
Those are my suggestions. I hope they were helpful.