I lost 10lbs the first week I started dieting.  I didn't think it was water, as I drank much more that week, but I've been told that's normal: you drink a lot, your body doesn't feel the need to retain as much, you actually lose water weight by drinking more.
Since then it was at most 2lbs per week, and then I hit the plateau after about 20lbs (another normal aspect of dieting apparently), so I've wavered at X lbs +/- 2lbs for about 3 months now.  I've just reacquired the gym-going habit, so I hope that kicks the losses back in.