The Camelbak hydration system has been used by military and outdoor enthusiasts for years, but the rarely make an appearance at the range. Their utility lies in a flexible bladder that can be carried on the back. Water is accessed through rubber straw that lies on the chest when not in use.
The Camelbak can be used on the range, and offers a great many advantages. Of course, if it is hot, you have water right with you and no reason not to drink. Having a small backpack can also allow you to keep large bottles off your belt, leaving more room for training equipment. Finally, if you can add a small, frozen cold pack to the pouch holding the bladder, you can keep your water and back cool all day long.