Cat Drinking a Lot of Water? Causes and When to Call the Vet

Yes, a cat can drink too much water, and when the bowl starts emptying faster with no obvious reason, it usually points to a medical problem. Kidney disease, diabetes and an overactive thyroid are among the most common causes, especially in older cats. All three are easier to manage when they are found early, so a clear rise in thirst deserves a vet visit, not a wait-and-see.

One exception jumps the queue: a male cat who strains in the litter box and passes little or no urine needs a vet right now.

Vets call increased thirst polydipsia and increased urination polyuria. They almost always travel together: a cat that pees out more water has to drink more to keep up, which is why your vet will ask about the litter box as well as the bowl.

How much water should a cat drink?

The Cornell Feline Health Center puts a cat's daily need at about 4 ounces of water per 5 pounds of lean body weight. For an average 10-pound cat, that is about one cup a day.

That cup is the total, not just what comes out of the bowl. Wet food can be up to 80% water, so a cat on canned food may barely touch the bowl and still be well hydrated. A cat on dry food gets more of its water by drinking. Compare your cat with itself, on the same diet, rather than with a number on a chart.

Where "too much" starts

Vets use different cutoffs, and the published numbers don't agree:

• A Royal Veterinary College specialist, writing in WSAVA congress proceedings, says more than about 50 ml per kilogram of body weight per day is probably excessive in cats.
• A UC Davis internal medicine specialist, in earlier WSAVA proceedings, puts the line at more than 100 ml/kg per day in dogs and cats.

The lower figure sits close to Cornell's average, so no single number settles it for your cat. Your vet interprets the measurement alongside blood and urine results. At home, watch for a clear rise over what your cat normally drinks that lasts more than a day or two. Exercise and hot weather can make a healthy animal drink more, according to the same RVC paper, and so can a switch to dry food. If none of those explains it, call your vet and bring your numbers.

Signs your cat is drinking more than usual

You may not measure anything at first. Owners usually notice it like this:

• You refill the bowl more often, or it is empty when it never used to be.
• Your cat visits the bowl more often or stays there longer.
• New water sources: the faucet, the shower, a glass on the nightstand, the toilet.
• More trips to the litter box, or bigger and more frequent urine clumps.
• Urine outside the litter box.

Treat urine outside the box as a medical clue until a vet says otherwise.

The big three causes

These are among the most common causes in middle-aged and older cats. Appetite and weight are the fastest way to tell them apart at home: diabetes and hyperthyroidism usually bring a big appetite with weight loss, while kidney disease more often brings a poor appetite.

Kidney disease

Chronic kidney disease (CKD) is one of the most common diseases of older cats. Cornell estimates it affects up to 40% of cats over 10 and 80% of cats over 15. Damaged kidneys can't concentrate urine, so the cat loses more water and drinks to make up for it.

According to the Merck Veterinary Manual, extra thirst and urination often don't show until about two-thirds of the kidney tissue has stopped working. So by the time you notice the bowl, the disease has already been building for a while. Weight loss, a poor appetite, lethargy and an unkempt coat can follow. Cornell notes that earlier diagnosis gives a cat the best chance at a longer, healthier life, which is why a thirsty senior cat should be checked. More in our guide to kidney disease in cats.

Diabetes

In diabetic cats, sugar spills into the urine and pulls water with it. The classic picture, per Cornell, is weight loss despite a good appetite, plus increased thirst and urination. Overweight, inactive, older and male cats are at higher risk.

Many diabetic cats can go into remission when treatment starts early, so a quick diagnosis matters. Diabetes can also tip into diabetic ketoacidosis (DKA), an emergency. The Merck Veterinary Manual lists its signs as increased thirst and urination with lethargy, weakness, a reduced appetite and trouble breathing.

Hyperthyroidism

An overactive thyroid gland speeds up the whole body. It mostly affects middle-aged and older cats. The usual signs are weight loss, a bigger appetite and more drinking and peeing; some cats also vomit, have diarrhea, act restless or develop a greasy or matted coat. Most hyperthyroid cats have a high T4 on a blood test, although a few need extra tests. Treatment options include medication (see our post on methimazole for cats), radioactive iodine, surgery or an iodine-restricted diet, and your vet will also check the heart and kidneys.

Other causes of increased thirst

• Urinary tract problems. Infection is one cause of lower urinary tract disease, which can show as straining, frequent small trips, blood in the urine or peeing outside the box. In male cats, straining with little or no urine can mean a blocked urethra, which Cornell calls a true medical emergency. See feline lower urinary tract disease.

• Liver disease. Signs can include increased thirst and urination, a poor appetite, vomiting, weight loss and jaundice (yellow gums, skin or whites of the eyes). Some cats show no signs.
• Medicines. Diuretics increase water loss. Long-term steroid treatment can raise thirst and urination too, although Merck notes that cats are less susceptible than dogs to steroid side effects. If your cat started a new medicine recently, ask your vet whether it could explain the change, and never stop a prescribed medicine on your own.
• Fluid losses. Vomiting and diarrhea drain water, and a cat may drink more to replace it. Both are reasons to call your vet on their own.
• Diet, exercise and heat. A switch from wet to dry food raises bowl drinking because the food no longer supplies much water. Exercise and hot weather can nudge intake up too.

Less common causes your vet may look for include high blood calcium and, in unspayed females, a uterine infection.

How to measure your cat's water at home

A home measurement tells your vet more than one taken at the clinic, because cats may drink less in an unfamiliar place.

1. Pour a measured amount of water into the bowl (a kitchen measuring cup works).
2. Twenty-four hours later, measure what is left. The difference is what your cat drank, give or take a little evaporation.
3. Write it down with your cat's diet (wet, dry or mixed) and any treats or food changes.
4. If you can, repeat it on a couple more days so one warm afternoon doesn't skew the picture.
5. Note how often you refill the bowl and anything else you see: appetite, weight, litter box trips, urine outside the box.

Several pets, one bowl? Then the measurement covers the whole household. Don't lock your cat away to test it; tell your vet you share a bowl. How often you refill it is still a useful rough guide.

What your vet will check

Expect a full physical exam, a weight check and questions about diet, medicines and other changes. Then, usually:

A stressed cat can have a short-term rise in blood sugar at the clinic, which is one reason vets don't diagnose diabetes from a single reading. Your vet may ask you to bring a urine sample; here is how to get a urine sample from a cat. Ask the clinic how they want it collected and stored before you start.

What to bring: your 24-hour water numbers, your cat's diet, a list of medicines and supplements, any previous weights, and a note of when you first noticed the change.

When to call the vet

Call now (emergency):

• A male cat straining in the litter box with little or no urine. A complete blockage can kill a cat in less than 24 to 48 hours.
• A thirsty cat, or a known diabetic cat, that is weak, lethargic, eating much less or having trouble breathing (possible diabetic ketoacidosis).

See your vet soon (within a few days):

• Drinking clearly more than usual for more than a day or two with no obvious reason.
• Increased thirst together with weight loss, a change in appetite, vomiting, diarrhea or urine outside the litter box.
• Any older cat that starts drinking more.

Mention at your next visit:

• A small rise that started right after a known change, such as switching to dry food, and has not grown. If it keeps climbing, move it up to "See your vet soon".

Quick answers

My cat eats wet food and barely drinks. Is that a problem? Usually not. Wet food can supply most of a cat's water. A sudden increase in drinking on the same wet diet is the thing to watch.

Should I limit how much water my cat drinks? No. Most of these conditions make a cat lose extra water, so keep fresh water available and let your vet find the cause.

Originally written by Alianna Munakata. Updated by the I Love Veterinary editorial team.

Sources

• Cornell Feline Health Center: Hydration
• Cornell Feline Health Center: Chronic Kidney Disease
• Cornell Feline Health Center: Feline Diabetes
• Cornell Feline Health Center: Hyperthyroidism in Cats
• Cornell Feline Health Center: Feline Lower Urinary Tract Disease
• Merck Veterinary Manual: Renal Dysfunction in Dogs and Cats
• Merck Veterinary Manual: Disorders of the Pancreas in Cats
• Merck Veterinary Manual: Disorders of the Liver and Gallbladder in Cats
• Merck Veterinary Manual: Corticosteroids in Animals
• Merck Veterinary Manual: Cushing Disease in Animals
• Nelson RW: Polyuria, Polydipsia and Diabetes Insipidus (WSAVA 2002, VIN)
• Church DB: Logical Approach to Polyuria and Polydipsia (WSAVA 2009, VIN)

This article is for general information and is not a substitute for advice from your veterinarian.