Water gets less attention than food and matters just as much, and the question owners ask — how much is enough — has a rough answer worth knowing and a more important one underneath it.
The rough figure, scaled to weight
As a rule of thumb, a healthy dog needs somewhere around fifty millilitres of water per kilogram of body weight over a day, and a cat is in a similar range. A bigger animal therefore needs proportionally more, and one eating wet food will drink noticeably less from the bowl because a large share of its water arrives in the meal. Treat that as a ballpark, not a target to pour down them — a pet self-regulates when water is freely available.
The change is the real signal
Far more telling than the exact volume is a shift away from what is normal for your particular animal. A dog or cat that suddenly drinks much more, or much less, than it usually does is worth a vet's attention, because a change in thirst is among the first outward signs of conditions from kidney disease to diabetes. Knowing your pet's ordinary intake is what lets you notice the day it changes.
Cats and the water they do not drink
Cats descend from desert hunters and carry a famously weak thirst drive, built to take most of their moisture from prey rather than a bowl. A cat living on dry food often does not make up the difference by drinking, which is one reason wet food, a water fountain, or several bowls placed away from the food can matter more for a cat than for a dog. If a cat is drinking far more than usual, that is the opposite worry and a reason to ring the vet.
How much water should a dog drink a day?
Roughly fifty millilitres per kilogram of body weight is a common rule of thumb, so a larger dog needs more and a wet-food eater drinks less. It is a ballpark; a healthy dog with water always available regulates itself.
My cat barely drinks — is that a problem?
Cats have a low thirst drive and take much of their water from food, so a cat on wet food may drink little and be fine. A cat on dry food that drinks little is worth helping with wet food or a fountain, and any sudden change in drinking is a reason to see the vet.
When should I worry about how much my pet drinks?
When it clearly changes from that animal's normal — a marked rise or fall in thirst is one of the earliest signs of several illnesses, so it is worth a vet call rather than a wait.