You have noticed the water bowl emptying faster, and every page you have found says “about an ounce per pound” and stops there. That is not enough to decide anything, because it gives you no way to tell an ordinary hot week from the thing a vet would want to see.
This page does three things instead. It works out what your animal actually needs from the maintenance formulas in the Merck Veterinary Manual, showing the arithmetic. It expresses what you measured as a multiple of that, because a multiple is interpretable and a raw number is not. And it explains how to measure 24 hours properly - the step that decides whether any of it means anything, and the one nobody covers.
It also tells you where the published evidence runs out, which is the part we care most about getting right.
How much should your pet be drinking?
Enter a weight and a measured 24-hour intake, and this works out what your animal drank per kilogram, sets it against the maintenance requirement published in the Merck Veterinary Manual, and shows the arithmetic so you can check it. It is built for the moment you have noticed the bowl emptying faster and want to know whether that is worth a phone call.
Questions people ask when the bowl keeps emptying
How much water should a dog drink a day?
It depends on weight, and the honest answer is a band rather than a number. The Merck Veterinary Manual gives two maintenance formulas that both apply to a dog between 2 and 70 kg: 30 times body weight in kilograms plus 70, and 132 times body weight to the power 0.75. For a 20 kg dog those come out at 670 ml and 1,249 ml, which is a wide gap - and that gap is real, not an error. Treat the range as the maintenance band. What matters clinically is not hitting a precise figure but whether your dog is drinking far more than that band, and whether anything else changed at the same time.
How much water should a cat drink a day?
Merck’s feline maintenance formula is 80 times body weight in kilograms to the power 0.75, and the general formula of 30 times weight plus 70 also applies between 2 and 70 kg. For a 4 kg cat that is roughly 226 ml and 190 ml respectively. Cats on wet food will drink far less from the bowl than that and still be perfectly hydrated, because wet food is around three quarters water. A cat that suddenly starts drinking noticeably more is the situation worth acting on.
My dog is suddenly drinking a lot of water. What does it mean?
It means something changed, and the change is the signal rather than the volume. Heat, exercise, a switch from wet food to dry, and some medications all increase drinking legitimately. If none of those apply, increased drinking is one of the earliest signs vets look at, particularly alongside urinating more, accidents indoors, eating less, losing weight or vomiting. An unspayed female dog that starts drinking more needs to be seen urgently, because a womb infection is one of the causes and it is a surgical emergency. Measure a full 24 hours before you call - a measured figure changes the appointment completely.
How do I measure how much my dog drinks in 24 hours?
Fill the bowl from a measuring jug and write the number down, then 24 hours later pour what is left back into the jug; the difference is what was drunk. Four things ruin the measurement: other pets sharing the bowl, a water fountain or toilet or puddles as uncounted sources, evaporation in warm weather, and wet food. Separate your pets for the day, turn the fountain off and close the bathroom door, stand a second identical bowl somewhere unreachable to measure evaporation and subtract it, and note what food they are on. Do it two or three days running, because one day is an anecdote and the trend is what a vet can use.
What is the threshold for a dog drinking too much water?
You will see 100 ml per kilogram per day quoted very widely as the official line for polydipsia. We could not find that figure in the veterinary reference we are able to check, so we do not use it to give a verdict. What is published is the maintenance requirement, and normal urine volume, which Merck gives as 20 to 100 ml per kilogram per day for dogs and 10 to 20 for cats. Expressing intake as a multiple of the maintenance requirement is more honest than asserting a cut-off we cannot source, and drinking more together with producing more urine is the combination that actually gets investigated.
