Cats descend from desert animals and evolved to take most of their water from prey. A cat that drinks little is often behaving entirely normally. The problem is that this makes genuine dehydration easy to miss.

How much is normal

A cat on wet food may barely visit the water bowl at all, because tinned food is around three quarters water. A cat on dry food should be drinking noticeably more, because dry food is around one tenth water.

So the question is not simply how much your cat drinks, but whether that has changed, and what it is eating.

Checking for dehydration

Two checks you can do at home:

The gums. Lift the lip. Gums should feel wet and slippery. Dry or tacky gums suggest dehydration.

The skin tent. Lift the skin over the shoulders and let go. It should fall back immediately. If it stays tented for a moment, fluid is short. This test is less reliable in very thin and very old cats.

If either check is abnormal, do not spend the day trying to encourage drinking. Come in.

Getting more water in

Increase the proportion of wet food. This is by far the most effective change.
Move the water bowl away from the food and well away from the litter tray. Cats dislike drinking beside either.
Offer water in several places around the house.
Use a wide, shallow bowl. Many cats dislike their whiskers touching the sides.
Try a running water fountain; some cats strongly prefer moving water.
Change the water daily.

The opposite problem

Be equally alert to a cat that suddenly starts drinking much more than usual. Increased thirst is one of the earliest signs of kidney disease, diabetes and hyperthyroidism, and it is easy to dismiss as a warm week.

A cat that empties its bowl daily when it used to ignore it should be examined and have blood and urine tested.

When to come in

If your cat has drunk nothing for a day. If drinking little comes with vomiting, diarrhoea, lethargy or loss of appetite. If the gum or skin checks are abnormal. Or if drinking has changed sharply in either direction.