Along with Camelback, two other names are good for general purpose hydration systems, Gregory, and, I believe, Ultimate Directions. There are makers of more cycling- and sports-specific hydration systems out there, but these three companies seem to carry systems that allow for various amounts of carry capacity, in some cases, up to 22-2500 cubic inches. Mountainsmith has a smaller hydration pack, and Mountainsmith, Gregory, and Dana have accessory pockets or built-in systems for their larger packs.
I never believed how much water I could drink until I started using a hydration system. I used to hate stopping to dig out bottles, and found myself feeling more worn out at the end of the day. I find that with a hydration system of some sort, I drink a little less at a time, but much more frequently, and usually feel fresher at the end of the day. The "clear and copious" rule for proper hydration also applies here.
What would be really cool is if, say, a custom kydex maker expanded his repetoire a bit to include shoulder-strap sheaths and holders for use with larger packs and the smaller hydration systems. What a market! He could make a million bucks and give me a kickback for the great idea.
