Drink! is a Mac application that ensures you don't dehydrate at your computer. Drink! sits unobtrusively in your status bar showing a glass that slowly empties. You can configure Drink! to pop up visual and/or audible reminders so you keep hydrating those kidneys.
Benefits of using Drink! include a satisfied, well-hydrated body, happier kidneys, and (scientifically proven!) less grumpiness.