When I started riding for fitness before I learned my lessons about hydration, I would be 5 to 6 pounds lighter at the end of a hour or two of riding. Now even after three hours of riding I pretty much only differ by less than a pound. Though I don't check very often any more.
Even in the moderate temps I've been riding in this week, I still drink about 24 fluid ounces of my hydration mix every 50 minutes. My mix is mostly maltodextrin with a little bit of sugar or stevia to take the edge off along with a very tiny amount of electrolytes and kool-aid powder to give some flavor and color.