The basic rule for dogs and cats
Veterinary guidance for both species lands in the same place: about 50–60 ml of total water per kilogram of body weight per day, or around an ounce per pound. Small animals sit at the higher end of that range because they have more surface area relative to their size. The calculator uses the midpoint and shows a range either side, since healthy pets vary.
Why food changes everything
Wet and raw foods are around 75% water; a cat eating only pouches may drink very little and be perfectly hydrated. Dry kibble is under 10% water, so a kibble-fed animal has to drink nearly its whole requirement from the bowl. This is why the calculator asks about diet and splits the total into water from food and water to drink. Cats in particular evolved to get moisture from prey and have a weak thirst drive, which is why kibble-only cats are prone to urinary problems.
Heat and exercise
Dogs cool themselves mainly by panting, which loses a lot of water. A long hike or a hot afternoon can raise needs by half or more, so the calculator applies multipliers for both. Carry water on walks over half an hour in warm weather and offer it at every stop. The same principles that apply to people in hot weather apply to pets, except they can't tell you they're thirsty.
When drinking changes, pay attention
A pet drinking far more than this estimate for days on end, or one that stops drinking altogether, is showing one of the most useful early signs of illness a pet owner can catch. Measure what you put in the bowl for a couple of days and bring the numbers to your vet. For your own hydration, our daily water intake calculator does the same job for humans.
