Dr. Jennifer Coates said: “I’d like to take a look at this question in a couple of different ways. To begin with, I utilized a well-regarded “calculator” to define the amount of water a 10 pound, adult neutered dog and cat should take in per day. The results were:

  • For dogs: 348 +/- 70 mls/day
  • For cats: 261 +/- 52 mls/day

These results show that cats simply need much less water per pound of body weight in comparison to dogs.

Now let’s look at where our 10 pound cat can get that water. Approximately, per day, this cat needs 261 kcal of energy from food. (This is not just a typo, it’s in fact a general rule of thumb states that water needs in ml are the same as caloric needs in kcal.)”

She further added: “for our water calculations, I am going to use a major pet food manufacturer’s adult maintenance pussy cat’s foods (both dry and canned) as exemplary diets.

The dry food contains 502 kcal/cup. Therefore, the car should be eating around 0.52 cups a day. Typically, dry cat food contains around 10% water, therefore 0.52 cups of food would give 0.052 cups of water or 12.3 mls. Subtracting that from our 261 mls per day leaves us with 249 mls (or about one cup) of water that the cat needs to drink from a bowl per day.

The company’s canned food contains 88 kcal/85 g can, so our kitty should be eating about three cans (these are tiny cans!) per day (88 x 3 = 264 kcal). The majority of canned cat food contain between 68 and 78 percent of water. I’ll use the average of 73% here. So, 73% of 85 grams times 3 is 186 grams of water, which equals 186 mls of water. Taking away 186 mls from the cat’s 261 mls total daily water need, leaves 75 mls (or approximately one third of a cup).

Is your brain spinning from all that math? Sorry! What you should understand is that when cats eat dry food, they need to get almost all of their water from other sources rather than their food, while a canned food only diet can supply around two-thirds of a cat’s needs.

This difference could be critical if cats truly do have a low thirst drive … more on this (and less math!) next week.”