My yearling bucks are expeirencing similar conditions, although I think I know why, It is because they are sniffing my breeder does on the other side of the shade cloth. These several bucks normally eat a full 5 gallon bucket a day (about 34lbs.) But during most of November they were eating a 5 gallon bucket every 4-6 days, their feed drop off unbelieveable! And during that time they were drinking my tub that holds at least 60 gallons, probably more, almost down to empty in 2 days. Probably for the most part because winter weather has not hit yet, we have been averaging 50 degrees during November, very warm. I did not do the math, but I am sure some of my bucks were drinking 5 gallons a day. Being a deer on a sunny 50 degree day with a full winter coat, would have to be similar to us dressing head to toe in a wool hunting suit on a warm day and walking around all day, I am sure we would drink a lot more that usual.
If you haven't noticed any health issues, I would say that your buck is just a bit lovesick this month, just my opinion, and I would suspect that he will return to normal feeding and watering in a short time, as most of the does are bred and not smelling as "sweet" to them anymore. I think bucks are on the move constantly this time of year(wild and pen bucks) even if your buck can't see your does, I am sure he is smelling them, or wild does.
As far as the 16%, I think that is good mix, in fact I never go above 16% protein at any time during the year, works fine for me. Good luck with him, I hope he stays well and gets no health issues.