Anytime you see a real increase in thirst/drinking and urinating, the 2 things you truly need to consider ruling out are Cushings Disease and Diabetes. Testing for diabetes is easy. Testing for Cushings is much more involved. The very 1st test you'd do to rule out Cushings (a test which is NOT diagnostic, btw) is the Cortisol-Creatinine Ratio Urine Test. This test does *not* tell you if Cushings is present, it tells you whether you need to proceed, or not, with the more specific and expensive Cushings tests (ie, the ACTH or LDDS etc).
Are there *any* other random symptoms...?
Here is a site on Cushings:
Cushings (Hyperadrenocorticism) | | Long Beach Animal Hospital