Hi Fister, how's it going?

Well, good news the lab work is all normal!

Could it be he has a bit of arthritis and drinking from a glass is no longer a comfortable position for him? If he is not getting dehydrated, then he IS getting the fluids he needs. And this could be from the fountain, as you say you don't know if / when he uses that. Or maybe he just decided he prefers the flowing water?

Seems you can sit back and relax, and THAT is a nice thing!