Cats are generally picky eaters, once they get used to a particular food it can be really difficult to get them to switch over to something new. I know it seems intuitive that an animal would want variety, but it can actually be a huge shock to their system to switch between a bunch of different foods (dogs and cats). It's often not a problem to move between similar formulations in the same brand, but changing foods often is a known cause of GI issues.
My cat (5 years old this summer) eats MCRC Adult, it's the veterinary formulation of Royal Canin. I feed her the dry, but I really should see about switching to the wet. Kidney failure is a common cause of death in elderly cats, and naasfu's right that in most cases the wet foods are better for the animal.
In terms of water, cats don't like to drink from deep water dishes, they like to be able to see what's going on around them as they are drinking. Using a shallow dish for water, or filling it almost to the brim can be used to encourage a cat to drink.