If you have a picky eater, it might not be the type of food you're feeding. And have you ever noticed your cat will chow down on a favored food and then all of a sudden turn his nose up at it? Cats live through their noses. They can smell bacteria starting to grow in food, and will never drink contaminated water. Have you gone to change the water bowl and felt that slimy coating on the bowl?
That's bacteria growing and they can smell it. We need to get as much hydration as possible in our cats so keeping the water bowl super clean at least daily, is vital! I like to use stainless steel bowls because it's harder for bacteria to grow on it versus plastic bowls.
Clean with mild dish soap and hot water before you add more food - even dry food - and as you change/add to the water. Be sure to RINSE many times (at least four) after you wash because they also don't like the smell or taste of soap.