Never force your hamster to fast, but if you want to know how long it can go without food and water, the answer is 1 to 4 days. This will depend on your hamster's health and age, as older hamsters tend to resist hunger and thirst less than younger ones. Hamsters will only be able to go two days without water when it is hot in the summer, so make sure your hamster's water bottle is always full of fresh, clean water.