Guinea pigs are not the tidiest pets you can have, which means a metal or ceramic water dish on the floor of their cage is not a good idea. Even without meaning to, your cavies can knock over the bowl, soaking their bedding. They can also push food or bedding into the water, making it unfit to drink. Hanging a cage-specific water bottle on the side of the cage is a cleaner, better option, but your guinea pig may need help adjusting to it.
Prepare the water bottle. Once you purchase a cage water bottle kit from the store, you will need to wash it. Use liquid dish soap and warm water. Rinse thoroughly and dry the outside. Fill with cool, fresh water.
Hook the water bottle to the cage. With the wire loop or other hardware included in the kit, attach the water bottle so the spout is inside your guinea pig's cage. Adjust the height of the bottom of the spout so it's low enough for your pet to easily reach. Remove the water bowl from the cage so your guinea pig won't expect water to appear in it.
Teach your guinea pig how to drink. Gently bring your guinea pig over to the new water bottle spout. Tap the metal ball at the end of the spout with your finger to release some water. If the guinea pig gets a little water on it, this will teach it that the spout is a source of water. Watch your guinea pig for a while. If, after an hour or so it hasn't tried the water bottle spout itself, take it back and show it again. This time try to get some of the released water on its mouth. It should be able to smell the water and figure it out eventually.