How Much Water a Dog or Cat Should Drink
How much a pet drinks is one of the more useful things an owner can know, because a sustained change in it is an early sign of several conditions — and you can only notice a change if you know the baseline.
Roughly body weight times a number
A healthy dog needs somewhere around 50–60 ml per kilogram per day. The water intake calculator puts a 20 kg dog at 1,000–1,200 ml — about a litre, or roughly four and a half cups.
Cats sit a little lower per kilogram, partly because they evolved to draw more water from prey. A 4.5 kg cat comes out around 203–248 ml a day, under a cup.
That figure includes food
An important qualification: this is total water, not water from the bowl. Wet food is roughly three-quarters water, so a cat eating mostly wet food may drink very little from a bowl and still be perfectly hydrated.
Switching a cat from wet to dry food therefore produces a large apparent increase in drinking that is not a change in total intake at all. Knowing that prevents an unnecessary worry — and, more usefully, prevents a real change being dismissed as a food change.
Measuring it properly
Fill the bowl with a measured amount, top it up with measured amounts, and note what is left after 24 hours. Do it over two or three days, since day-to-day variation is normal.
In a multi-pet household this needs separating the animals, at least for the measurement period. It is fiddly, and it is the only way to get a figure for a specific animal.
What moves it legitimately
Heat, exercise, a switch from wet to dry food, lactation, and several medications all raise intake, and none is a cause for concern on its own. A dog after a long summer walk will drink far more than its calculated baseline.
What matters is a change that persists once the obvious explanation is excluded.
When to call
A sustained, unexplained increase in drinking and urinating is a classic early sign of kidney disease, diabetes, and several hormonal conditions, and it often shows up before anything else does. In an older cat especially, it is one of the most valuable things an owner can spot.
A marked decrease matters too, and dehydration in a small animal develops quickly — particularly alongside vomiting or diarrhoea.
Either way, a persistent change is a phone call. Take your measured figure with you: “he is drinking about two litres a day, and his baseline was one” is far more useful to a vet than “he seems to be drinking more”.
Encouraging a cat to drink
Cats are famously indifferent to water bowls, which matters because urinary problems are common in cats. Several things help: more bowls in more places, away from food and litter; wide shallow bowls rather than deep narrow ones; a water fountain, which many cats prefer to still water; and wet food, which is the single most effective change.
Move the bowl away from the food, too. It is a small thing that a surprising number of cats respond to.
General information, not veterinary advice. A sudden or sustained change in drinking is a reason to call your vet.
Daily intake by weight
| Weight | Dog, per day | Dog, in cups | Cat, per day |
|---|---|---|---|
| 5 kg | 250–300 ml | 1.2 | 250 ml |
| 10 kg | 500–600 ml | 2.3 | 500 ml |
| 20 kg | 1,000–1,200 ml | 4.6 | 1,000 ml |
| 30 kg | 1,500–1,800 ml | 6.9 | 1,500 ml |
| 40 kg | 2,000–2,400 ml | 9.2 | 2,000 ml |
A 20 kg dog drinks roughly 1,100 ml a day — about 4.6 cups. A 4 kg cat drinks around 200 ml.
Why the range matters more than the midpoint
The figures are a band rather than a target, because intake varies legitimately with diet, weather and activity. A pet on wet food drinks far less from the bowl because most of the water arrives in the food — often 70–80% moisture against under 10% in dry.
So a cat eating wet food and barely touching the water bowl is usually normal, and the same cat switching to dry and not increasing its drinking is not.
The change is the signal, not the number
This is the part worth taking seriously. A pet that has always drunk at the low end and still does is simply that pet. A pet whose intake has clearly increased or dropped over days or weeks has changed, and that change is worth a vet's attention.
Increased drinking and increased urinating together are a well-recognised reason to book an appointment — not because the calculator says so, but because several conditions that vets can test for present that way.
Measuring it without guessing
Fill the bowl with a measured amount, top it up with measured amounts, and note the total over 24 hours. Do it for three days and take the average, because a single day tells you very little.
In a multi-pet household, measure separately where you can. Shared bowls make individual intake unknowable, which matters precisely when you are trying to work out whether one animal has changed.
Encouraging a pet that drinks too little
More bowls in more places, away from food and litter. Wider bowls for cats with sensitive whiskers. A running fountain, which many cats prefer markedly. Adding water to wet food.
All of these are cheap and none of them is a treatment. A pet that will not drink, or that suddenly stops, needs a vet rather than a better bowl.
The three-day measurement
It costs nothing, takes a jug, and turns the vaguest thing an owner can report into one of the most useful numbers they can bring to an appointment.
Do it once while everything is normal, so you know what normal looks like for your own animal. A baseline collected in advance is worth far more than the same measurement taken for the first time when something already seems wrong.
This is general information, not veterinary advice. Every figure here is a starting point for a conversation with your own vet, who knows the animal in front of them. Anything sudden, painful, or getting worse is a call to a clinic rather than a calculation.