Cats are "desert species" by nature meaning that they often require less water for maintenance of their body functions. They have very efficient kidneys which work to conserve water (as long as the kidneys are healthy).Cats' prey in the wild is often 70%-80% water so that they very seldom will drink water by itself in the wild unless overheated. Most canned foods match this as well. Most dry foods however are about 8% water. Fresh palatable water must be readily available at all times if feeding a dry food. Cats daily still need about 20-30 ml/pound of body weight per day, but this is combined intake of food and water moisture.

Cats do not have a very strong thirst drive. This often means that they have a more difficult time adjusting for excess water loss from heat than dogs do. Even when offered water, cats on dry food often do not drink enough water to make up for what is lacking in the diet. When you combine water intake from food and water, the cat on dry food often takes in about half of what the cat on canned food takes in per day. Cats increase voluntary water intake when fed dry food but not in sufficient amounts to fully compensate for the lower moisture content of the food. In a recent study, cats consuming a diet containing 10% moisture with free access to drinking water had an average daily urine volume of 63 milliliters (ml). This volume increased to 112 ml/day when fed a canned diet with a moisture content of 75%. Several studies have shown that dry cat foods contribute to decreased fluid intake and urine volume. These often lead to kidney disease, kidney failure, or urinary crystal/stone production.

So, ideally, canned cat food is actually more beneficial to cats as it most closely mimics the diet they would get in the wild. It is higher in protein and water and lower in carbohydrates ... just like a mouse. Can a cat be maintained on dry food? Yes it can, but it is at higher risk for obesity, diabetes, and urinary tract disease. More specifics on dry vs. canned food for your cat should be addressed one to one with your veterinarian.