Although in the wild hamsters are desert animals in most cases, and do not need to drink a lot of water you need to make sure it is readily available at all times. Change it every 1-2 days and make sure the bottle is working properly, easy enough.
The only time you need to worry about how much/little your hamster is consuming is if you have a dwarf species and they start drinking A LOT of water. This is one of the signs of diabetes in our little friends, and one of the things I noticed about Little Man that suggested he had it :(.
Another use for water is obviously baths, so I will take a moment to mention that you should NEVER EVER bath your hamster in water. It doesn't need it, doesn't like it and can be dangerous for them. Give them dishes with chinchilla sand instead and they will bathe them selves :).