The Water Rover is the most ingenious invention we've seen to carry your little dog's water supply! The Water Rover even has a patent in the U.S. The large bottle holds 15 ounces, the small bottle holds 8 ounces. The cap has a built-in belt clip, so no hands are needed to carry the Water Rover! To fill the Water Rover, just unscrew the wide-mouth cap and fill with water and perhaps some ice on a hot day. When your pup needs water, just pull out the stopper and put the Water Rover down. You can store the stopper behind the belt clip. When your dog's done drinking, just tilt the water back into the bottle, pop in the stopper, and away you go!