HI fkftcsward,
The dog could have a urinary tract infection as this will show an increase in water intake and in urination. You may also notice straining to urinate or blood in the urine. Here is more on this. This site will tell you symptoms, causes and treatments. http://www.petplace.com/dogs/acute-cystitis-in-dogs/page1.aspx
Also this breed is prone to renal kidney kidney failure and diabetes. Both of these would show an increase in water intake and output as well as lethargy, bad breath, vomiting, lack of appetite or depression.
Kidney failure http://www.petplace.com/dogs/chronic-renal-kidney-failure-in-dogs/page1.aspx
Diabetes would show increase in thirst, lethargy weight loss frequency of urination, and possible blindness. http://www.petplace.com/dogs/diabetes-in-dogs/page1.aspx
I would have the dog checked by a vet and bring in a urine sample for testing. A blood count may also have to be done if it is not a urinary tract infection.
Here is more on the breed and its prone illnesses.
http://www.petplace.com/dogs/choosing-a-rottweiler/page2.aspx
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24 years training & behavior, Therapy dog eval, Newfoundland breed plus, PA Animal Response Team