In many ways and places throughout this site you will hear me "preach" ample hydration for cats. I cant stress enough: it is VERY important your cat gets enough water.
A cat's average daily water requirement ranges from 5-10 fl. oz. Canned food provides much of a cat's daily water needs; canned food contains 70-80% water, whereas dry food is only 7-10% water. Cats should be fed a minimum of 60% canned food to dry kibble. A diet of only dry kibble can lead to a lifetime of mild dehydration and eventual renal issues.