At my gym, you are required to bring water to a spin class, because an hour of profuse sweating means you are going to have to sip regularly to stay hydrated. But here's a thought: Make sure you start you workout well hydrated. This will seriously improve your performance and help your precious bottle of water last a little longer during your workout.
To do this you need to stay hydrated during the nonexercise times of your day, and if you exercise daily you will be drinking more than the average sedentary Joe or Jane. Lance Armstrong's coach Chris Carmichael recommends drinking around a gallon of water a day – that's 128 ounces – not including the fluids you drink while exercising. If you are planning on sweating later, go ahead and drink up now.