If at all possible, and there are instructions for making this homemade and cheap on the site, getting a pet fountain. Back when I didn't have a cat fountain I noticed Ping hardly ever drank water out of the bowl of still water. But once I got the fountain he would drink regularly from that even with wet food in his diet. May be that is something you can look into.
Do you mean pinch the scruff and see if it snaps back? Yes, I don't know if I'm doing it right though. The skin seems to go back quickly and "normally" but then again I have nothing to compare to.
I change the water twice daily in a big heavy glass bowl. It's about 40oz of water that gets poured out since no one touches it.