This is the part I find very pertinent: to quote from the article on water requirements section on Feline Nutrition from Max's House (see link in message above):
"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%. Urine specific gravity was also higher in cats that were fed the low-moisture food. Decreased urine volume may be an important risk factor for the development of urolithiasis in cats. Diets that cause a decrease in total fluid turnover can result in decreased urine volume and increased urine concentration, both of which may contribute to urinary tract disease in cats. Several studies have shown that dry cat foods contribute to decreased fluid intake and urine volume
Homeostatic control of water balance in cats differs in some important respects from that of dogs Cats make less precise and rapid compensatory changes in voluntary water intake than dogs in response to changes in the water content of their food. Similarly, their compensatory drinking response to dehydration due to increased environmental temperature is less effective than dogs. This apparent weakness of the cat's thirst drive to respond to changes in her state of hydration has led to the conclusion that feeding canned food assures adequate hydration at all times
The emphasis is mine. I'd do the research for you, but I honestly do not have the time. Check out Littlebigcat.com as well as www.catinfo.org
(a vet written site) for more on cat nutrition, and I think touching on water requirements, value of dry food vs canned re moisture content etc.