I was thinking diabetis insepidus also. The reason I even know about that is because my girl did the same thing. It was diagnosed as spay incontenence and we tried Proin but didn't help and caused terrrible side effects. I ended up taking her off it and putting her in a diaper. Vet wanted to run some tests that were not very pleasant sounding and the medicine for it was outrageous. I elected to just go with the diapers but she has since stopped drinking gallons like she used to. Not sure really why the change but my first thought was she was put on a raw diet about two years ago and seemed to slowly improve over time.
Rusti EAC, TN-N, TG-O, WV-N, NCC, NJC, CGC, GSD Diva
Jerry Lee AXP, MJP, OAC, TN-N, WV-N, NCC, NJC, SPJ, UAG1