Cat Water Intake

To determine the necessary calorie intake for a cat, the formula is 1.2 x the resting energy requirement (RER), which is roughly 1.2 x 70 calories/kg of body weight. 

Using this formula, an 11 lb cat (5kg) would need 420 calories per day and therefore about 420ml of water. (5 Kg x 70 calories x 1.2 = 420)

Some water is obtained through the food and the amount varies by composition of the food (canned food might be 80% water and dry food 5% water, for instance).

The variability in water need based on diet can be very large and is a source of confusion. Cats being fed dry food are reported to require approximately 2.5 x the volume of dry food for water intake.

So if the cat is eating 1 cup of dry food per day it requires approximately 2.5 cups of water per day.  Cats being fed canned food can sometimes nearly meet their water intake requirements from the food alone.

With these things in mind, the answer to your question from a clinical standpoint comes down to this. If you are observing an increase in your cat's water intake and everything else in his or her life is about the same, there is a really good chance that the problem is polydipsia or a real increase in the need to take in water.

This should be reported to your vet and screening tests to rule out the most common problems leading to excessive water intake considered. A urine sample can sometimes rule out diabetes and kidney failure, two of the most common causes. Routine blood chemistry examination and cell counts can help rule out liver failure, kidney failure, diabetes, hypercalcemia and polycythemia as potential causes.