Obviously, you have to do what works best for you. I've found that it all comes down to personal philosophy and experience--for us and for the people who care for our pets.
I'll ask 5 people (drs. and techs) the same question and get 6 different answers. It's crazy. Some people are more by-the-book/ scientific, some are more holistic, and others are more old-school/ loosey-goosey. And these are all people that I respect immensely.
So, I do what has worked for me--so far, so good. I've always fed high end dry food, primarily, and it's worked for me. I just brought my 14 year old cat into work for a regular senior physical and the doctor couldn't believe she was 14 years old because she seems to be in such excellent shape. I'll get her bloodwork and urinalysis results this week--fingers crossed.
But, I'd do some independent research on the dry vs. can food thing...in the practice I work at we recommend kibble over can as the primary food source.
In regards to water consumption--this might sound weird but, is your cat's water bowl plastic? I've found that my cats turn their nose up to food or water served in plastic. I provide fresh Brita-filtered water in a ceramic bowl. I'm pretty well-trained :o)
Best Regards,
Good luck with your cat. My 10 year old perfectly healthy cat (who dines 90% dry food) was just diagnosed with Hyper-T. We're presently adjusting her meds for thyroid and to see the kidney damage....then hopefully it's on the I-131.