Definitely just water weight! When you lose weight, you need to drink extra water so that your body will let the excess water weight out, and so that the products of fat-burning, which are harmful, will be flushed out of your body. Once you start drinking enough water again, I'll bet dollars to low-carb whole-wheat sugar-free donuts that you'll see an enormous difference in the scale.
(Boy, low-carb whole-wheat sugar-free donuts don't sound terribly appealing, do they?)
And to emphasize -- if you know you're on the right track, don't worry about what the scale is telling you. That number is less important than if you are moving in the right direction to your own better health.