How much should they drink?

The range comes from figures commonly quoted for healthy adult pets: about 50 to 65 milliliters per kilogram a day for dogs, which is the familiar ounce per pound, and about 40 to 60 for cats. It is a total from all sources, so a pet on wet food drinks far less from the bowl than one on dry.

To find out what your own pet drinks, fill the bowl with a measured amount in the morning, measure what is left 24 hours later, and repeat for three days. It is harder with several pets or a cat that drinks from the tap, but even a rough figure is worth having.

In an older pet, a rise in thirst is one of the most common early signs of illness, and it often shows up before anything else. If your pet is drinking clearly more than before, take your measurements to the vet. And leave the water down: limiting it does not treat the cause and can make a sick pet much worse.