Buying a water bottle & using the kitchen or water machine at your office, paid for or otherwise, will save money in the end. Not to mention the environment. It'll remind you when it's empty to refill it, get one with oz & keep track of your intake.
Joining a waterclub is a good way to tell others in your office to join in too. If there is no water club, just be a cool kid with a reusable bottle. They are fun to decorate, and easy to find!