Like all pets, your hamster needs access to clean drinking water to stay hydrated -- otherwise he could become constipated or dehydrated. Make sure his water is fresh and his water delivery supply is clean and working properly.
The best way to give your hamster clean, fresh water is with a gravity-fed water bottle that has a sipper tube or spout. The bottle attaches to the outside of the cage, and the curved drinking tube goes through the bars at mouth height so your hamster can easily drink. If your hamster is in a terrarium or molded housing, the bottle can hang inside the enclosure from a hook or fixed to the side wall with a piece of hook-and-loop fastener. These bottles come in different sizes for various pets, but the small mouse or hamster size works well.
Make it Clean
If your hamster is not drinking, first make sure the water is fresh and the bottle is clean and soap-free. If it's dirty or has soap residue, he will probably not drink. Wash and scrub his bottle thoroughly with soapy water and bleach it once a week, using a bottle brush for the inside and a smaller brush or pipe cleaner for the sipper tube. Rinse the bottle to remove all traces of soap and bleach, and fill it with fresh drinking water.
Make it Work
Once you're sure it's clean, make sure the bottle is working properly and your hamster knows how to access the water. Tap your finger gently on the end of the spout until a few drips of water appear. If the sipper tube contains a metal ball, move the ball up and down to ensure it has freedom of motion. Leave a drop of water at the end of the tube and chances are your hamster will find it and start to drink.
If your hamster won't drink from a water bottle, try a water dish instead. The dish should be heavy enough not to tip over but small and shallow enough not to present a drowning hazard, especially for baby hamsters. If the bowl is even big enough for the animal to accidentally become wet and chilled, he could become sick. A small ceramic bowl designed for hamsters works well.
Wash and Refill
Besides the drowning, spilling and chilling risks, another disadvantage to using a bowl is that your pet likely will kick litter and debris into his water dish by accident. Monitor, clean and refill his water on a daily basis.
In addition, like a bottle, the dish needs to be thoroughly scrubbed with soap and water every week and bleached to disinfect. If it's dishwasher safe, you can wash your bowl in the dishwasher, but manually scrub any debris that may be missed in the automatic cycle. Make sure it is rinsed completely and free of soap or bleach remnants before filling it with fresh water.
For temporary hydration, provide your hamster with a piece of green vegetable such as broccoli to eat.