The cat has evolved to obtain her water requirements almost entirely on the moisture content in her food - inherited from her desert-dwelling ancestors. Cats can live for long periods without drinking water when receiving food containing 67-73% water but become dehydrated when the water content of the food is 63% or less. Canned diets contain enough water that cats consuming them rarely need to drink. Daily water needs, in milliliters, often are "guesstimated" as equal to the metabolizable energy requirement in kilocalories or approximately 60 ml/kg. Once the diet is consumed, oxidation of nutrients produces an additional 10 to 13 grams of water for each 100 kcal of metabolizable energy. Thus a 4 kg cat consuming a 240 kcal canned diet containing 78% moisture will consume 237 ml or 98% of its daily water need directly from the diet. Thus the cat needs to drink less than 1 oz. of additional water per day whereas a cat consuming a 240 kcal dry diet needs to drink over 7 oz. of water per day. This can be difficult because cats are not naturally big drinkers. Feeding a canned diet containing 78% moisture virtually guarantees homeostatic control of water balance in the cat.