Top Fill Water Bottles (16oz.) are the next generation water bottle for guinea pigs. Top Fill Water Bottles feature an innovative bracket System that allows the Water Bottle to stay mounted to the outside of any wire cage. They also feature a unique top opening which allows for convenient cage-side refills. Simply flip open the top of the water bottle and refill the bottle cage-side with a water jug or filtered pitcher. Patent-Pending Sipper Tube is designed to ensure a drip-free Experience. This design even makes it easy to insert ice cubes into the water bottle during hot weather.