This is a question that I'm commonly asked and the answer is fairly straightforward.
As humans we naturally associate drink with food; all our meals are usually accompanied by a drink and even when watching TV or having a snack at the cinema we'll usually have a drink to go with it. It's therefore easy to understand why we put our cat's drinking bowl right next to their food. We imagine they'll enjoy a slurp of water to wash down the succulent pieces of ocean fish garnished rice and vegetables or some such other delicacy that we provide them with. However, in reality the truth is that cats simply don't associate food and water in the same way we do. When you think about it, if a cat is out hunting, it doesn't necessarily happen across a convenient pond or puddle right next to where it's caught it's prey! There is also a school of thought that the proximity of food to water, somehow taints the water as far as the cat is concerned.
So whilst, some cats will adapt to our choice of water bowl location, many will seek out water elsewhere, such as from a dripping tap, the toilet bowl, or the glass of water next to our bed.
So as with all cat resources it's important that we give them a choice about where they drink. One drinking bowl per cat plus one in separate locations is recommended. This is especially important for cats on a dry food only diet, or with any history of lower urinary tract disease or kidney problems. Water bowls should ideally be ceramic, wide-rimmed and filled to the brim with water so that cats don't get their whiskers wet. For those cats that like moving water, pet water fountains are a great idea!