For a dog or a cat, water is not a chemistry problem. It is a health signal. How much they drink is one of the few things you can watch at home that changes early when something is wrong, and a clear change in it is a reason to see a vet even when the animal looks well.
Less is published here than you would expect. The Merck Veterinary Manual gives a figure for mammals in general rather than for dogs: "In a thermoneutral environment, most mammalian species need ~44-66 mL/kg body weight." Cornell's Feline Health Center gives a cat figure, about four ounces per five pounds of lean body weight a day, so roughly a cup a day for a ten pound cat. That works out near 52 mL per kg.
The National Research Council's own booklet on dogs gives no milliliters per kilogram figure at all. It says instead that the need rises with exercise and "may more than double in warm conditions", which is the honest shape of the answer.
This is the rule everybody repeats. We went looking for who published it and found pet blogs, retailers and water bottle brands. No veterinary manual, no professional body and no National Research Council document states it. It happens to land at about 65 mL per kg, which is just inside Merck's range for mammals, which may be why nobody has ever questioned it.
A single day's measurement tells you very little, because intake moves with the weather, the food and the exercise. A sustained change tells you a lot.
The veterinary term for drinking too much is polydipsia. The figure used in practice, quoted in Today's Veterinary Practice from the standard endocrinology text, is water intake above 100 mL per kg per day, with urine output above 50 mL per kg per day. A separate reference by a veterinary nephrologist puts normal dog intake as "usually less than 60 mL/kg/day" with 100 as the upper limit.
For cats there is no validated number. The same nephrology reference says so in print: normal intake is "likely substantially less in cats, but a well-defined cutoff value has not been established". You will find 45 or 50 mL per kg quoted for cats on revision sites and summary pages. We could not trace either figure to a primary source, and the reference that addresses the question directly says it does not exist.
So for a cat the practical measure is not a threshold, it is your own baseline. If a cat that never drank starts emptying the bowl, that is the finding.
It is a real clinical sign with a short list of common causes. The stepwise diagnostic review in Today's Veterinary Practice names chronic kidney disease, diabetes mellitus, hyperadrenocorticism, hyperthyroidism in cats, high blood calcium, diabetes insipidus of both kinds, liver problems, kidney and urinary infection, and several less common conditions. The only drug groups it names are steroids and diuretics.
None of that is diagnosable at home, and that is the point of the page. A dog or cat that has clearly started drinking more, especially with more urinating, has a reason, and the common reasons are treatable and get worse while you wait.
Canned food is mostly water and dry food is nearly none of it. Merck gives the range: canned pet foods vary "from 60% to more than 87%" moisture, dry foods contain 3 to 11%, semi-moist 25 to 35%. So an animal on canned food takes in most of its water at the bowl of food and drinks less, and an animal on dry food has to make it all up by drinking.
The obvious question is whether they do. For cats, it has been measured, and the answer is no. In a study published in the British Journal of Nutrition, cats fed a dry diet took in 103.4 mL of fluid a day in total, while the same cats on a high moisture diet took in 144.7 mL. They drank more on the dry food and still ended up around 40 mL a day short, and their urine was measurably more concentrated.
The National Research Council describes the underlying reason without hedging: cats "don't drink as much per kilogram of body weight as do dogs, perhaps because of their evolution as desert animals", and where a dog will replace 6% of its body weight in water in an hour, a cat takes 24 hours to do the same. It calls the result a weak thirst drive and connects it to urinary stones.
This is the part of the subject with the largest gap between what is sold and what has been measured.
| Study or source | What it found |
|---|---|
| Grant, Journal of Feline Medicine and Surgery, 2010 | Cats drank more from a fountain, 31.6 against 22.9 mL per kg per day, but their urine was no more dilute. The paper concludes a fountain "failed to substantially increase water intake and dilute urine in cats". |
| Robbins and others, same journal, 2019 | Still, circulating and free-falling bowls: no meaningful difference between any of them. |
| Scoping review of 32 publications, Journal of Animal Science, 2026 | Records the effect of bowl or fountain type on intake as none. |
| Cornell Feline Health Center | "Some cats increase their intake of water when provided with water fountains, but individual preferences among cats for these varies." |
Cornell and the trials are not flatly contradicting each other. Cornell is saying some individual cats like them, which is true and is worth something if yours is one of them. The trials are saying that across a group, a fountain does not reliably produce the outcome people buy it for, which is more dilute urine.
For dogs there is no fountain trial at all. The only controlled study of dog bowls we found tested scent rather than movement.
The claim that cats prefer running water because instinct tells them still water is stagnant has no source we could find. It is a story attached to a product.
The skin tent test, pinching the skin over the shoulders to see how fast it falls back, is real and is used by vets. The 2024 AAHA fluid therapy guidelines grade dehydration by it, from "some change in skin turgor" at 5 to 6% up to a persistent skin tent at 10 to 12%. The same guidelines add the caveat in the same table: "There is substantial clinical variation in the correlation between clinical signs and degree of dehydration, so this is an estimate only."
It is least reliable in exactly the animals people worry about most. A veterinary review notes that skin turgor is reduced in thin and older animals whatever their hydration, and is often normal in young animals that are dehydrated, and that nothing below 5% dehydration is detectable on examination at all. Cornell gives the same warning for older cats.
Cornell's list of signs worth acting on is lethargy, weakness, poor appetite, dry gums, and in worse cases eyes that look sunken.
We could not find a veterinary or public health body that has published on whether pets should drink tap, filtered, bottled, distilled or softened water. Not Merck, not Cornell, not AAHA, not the RSPCA, not the National Research Council. Every page we found recommending filtered or bottled water for pets was published by a company selling filters or bottled water.
The one public health statement that exists is narrow and is about emergencies. The US Centers for Disease Control and Prevention, on drinking water advisories: "Give pets commercially bottled water or boiled water that has cooled." That applies when your supply is under an advisory, not on a normal day.
There is one piece of real research on the water pets actually drink. A study published in PLOS Water in 2025 tested the tap water in 178 households in the Dog Aging Project and found metals above EPA limits or health guidance in a substantial number of them. It is a finding worth knowing, and it is not a recommendation to buy anything.
There is no peer-reviewed study of bacteria in pet water bowls that we could find. There is one on dog food bowls, published in BMC Veterinary Research, which found metal bowls more contaminated than plastic and hand washing less effective than a dishwasher, and found no Salmonella, Campylobacter or verotoxigenic E. coli in 96 bowls.
The widely quoted claim that the pet bowl is the fourth germiest item in the house comes from a 2011 household study by a standards organization, covering 22 volunteer households, not peer reviewed, and lumping food and water bowls together. Wash the bowl daily because it is sensible, not because of that statistic.
This is where drinking stops being a general wellness subject. The 2025 international consensus guidelines on lower urinary tract disease in cats state that for the commonest form, feeding a wet diet and increasing water intake "may help to prevent recurrence", while noting studies remain inconclusive, and for calcium oxalate stones list increasing water intake among the preventive measures. Cornell, on chronic kidney disease, says maintaining good hydration "is essential", because dehydration speeds the damage.
If your cat has been diagnosed with either, water intake is part of the treatment and is worth discussing with your vet rather than solving with a purchase.
Those are the four signs of diabetes, and in dogs they arrive over days rather than months. What the 2026 guideline says about the signs, the diagnosis and the treatment: Diabetes in dogs.