I seldom see my chams drink but never show signs of dehydration. Humidity helps spot with keeping a cham hydrated and live plants, particularly the fast growing plants like pothos, help a lot with that. I also occasionally mist at night... Like nature would have it. They won't drink but can gain moisture from humidity.
Like Jared said, he a loop watcher. But don't freak out of where the white and brown meet is yellow, that just a little blending. But the rest of the white should be able white. Sunkin eyes and behavior are the other signs but by then you are talking defeat hydration.
If you haven't read already, fountains are a no-no. They harbor bacteria. In my opinion they are ok for a few days (afterwards you clean it, bleach it, dry it, pack it) like if you go on vacation or your cham is dehydrated, but not for daily use.