and Cathy Bickel
Any commercially available 4-8 ounce bottle should work for gerbils.
Gerbils housed in an aquarium will also need a metal holder from which the bottle will hang. The most important thing about water bottles is to make sure there is always water in the bottle.
Some gerbils are relentless water-bottle chewers. If one of your gerbils is a water-bottle chewer, position toys so that the gerbil cannot use them to climb up on top of the water bottle. Keep the water bottle high enough the she cannot sit on top of it (but low enough that she can drink. You may be forced to move up to more indestructible bottles and holders.
Another spot on the bottle where the gerbil may chew is around the bottom of the bottle. Small animal "bell bottles" have screw-on lids that cover the whole bottom of the bottle, and may come as a set with a matching metal chew guard which acts as a shield around the base of the bottle. If the bottle is instead the kind that is shaped like a cylinder, and the cap doesn't cover the entire base of the bottle, you will need to get one of the bottle holders with a metal base that acts as a shield around the lower part of the bottle. These holders should be located by the bottles in the store.
If you have a water-bottle chewer, keep an extra bottle on hand so that a destroyed bottle is not an emergency.
Water bottle hygiene is important for the health of your gerbils. Every time you fill the bottle, take out the rubber washer and rub it with your fingers to remove the film of bacteria that will build up. Every week, take the water bottle out and wash it with soap and water. Use a bottle brush to clean the inside. Stick your pinkie finger inside and run it along the flat edge at the bottom of the bottle, another place where gunk accumulates. You may want to rinse the bottles in a mild bleach solution, with about a tablespoon of bleach to a quart of water. After the bleach rinse, rinse it well again afterwards with just plain water until the bleach smell is gone.