How much water should your cat drink?

Where the figure comes from

An adult cat needs around 50 ml of water per kilo of body weight a day, usually somewhere between 40 and 60 depending on its activity, the heat and what it eats. That is total water: what it drinks plus what comes in its food. Dry food contains about 8 to 10 % water and wet food between 75 and 82 %, so a cat that eats only wet food can cover almost everything with its meals and hardly go near the water bowl. To work out what the food provides we estimate its daily calories from its weight and use typical densities for each type.

Why cats drink so little

The domestic cat descends from a desert cat used to getting almost all its water from its prey, and it has kept a weak thirst drive. On dry food, many drink a little less than they would need, and very concentrated urine is fertile ground for crystals, stones and cystitis. It helps to have water in several places, away from food and the litter tray, in wide bowls where its whiskers do not touch the sides, to change it every day and to try a fountain if it likes moving water. And, above all, to include wet food.

How to measure what it drinks

With a measuring jug. Fill the bowl with an exact amount in the morning and, 24 hours later, measure what is left. To allow for evaporation, put an identical bowl with the same amount next to it where the cat cannot drink, and subtract the difference. With a fountain, do the same with the reservoir. Repeat for two or three days, because one hot day or a day of play changes the figure. If several cats drink from the same place, the measurement covers all of them: it tells you whether it rises a lot, not who is drinking.

When drinking a lot is a symptom

Vets consider that a cat drinks too much (polydipsia) when its total water goes above about 100 ml per kilo a day. You notice it long before that: the bowl empties sooner, the litter clumps are bigger or more numerous, or the cat goes looking for taps and glasses. The most common causes are chronic kidney disease, diabetes and hyperthyroidism, and all three are diagnosed with blood and urine tests. The sooner they are caught, the better they are controlled, so do not wait for other symptoms to appear.

And when drinking little is a problem

A cat that suddenly stops drinking, and also stops eating or vomits, needs a vet the same day. If what you see is that it has always drunk little, check for signs of dehydration: dry or sticky gums, skin on the neck that is slow to fall back when gently pinched, and dry, hard stools. And watch out with males: if it goes in and out of the litter tray without peeing, or only passes a few drops, that is not a lack of water but a possible urinary blockage, and it is an emergency.