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Why Is My Cat Drinking So Much Water?

A cat that suddenly starts drinking much more water than usual — a condition called polydipsia — is almost always signalling an underlying medical problem. This is one of the most important symptoms for UK cat owners to recognise, as several serious but treatable conditions present this way.

How Much Water Should a Cat Drink?

Cats evolved as desert animals and historically obtained most of their moisture from prey. A cat fed primarily dry food will drink more water than one on a wet diet — this is normal. As a rough guide, a cat should drink approximately 40–60ml of water per kilogram of body weight per day, though this varies with diet.

The key signal to watch for is a change in drinking behaviour — a cat that previously ignored the water bowl and now seems to be drinking frequently, or one that starts seeking out unusual water sources (taps, bath edges, outdoor puddles) is likely polydipsic (drinking excessively).

In practice, most owners notice polydipsia because they're refilling the water bowl more than usual, or because they notice the cat at the water bowl repeatedly throughout the day. If you're unsure, measuring water intake over 24 hours can provide a useful baseline to share with your vet.

Diabetes Mellitus

Diabetes mellitus is one of the most common causes of polydipsia in cats, alongside excessive urination (polyuria). Unable to use glucose efficiently, the body produces large amounts of glucose-laden urine, pulling water with it and triggering thirst to compensate.

Signs alongside increased drinking include increased urination (perhaps using the litter tray more often, or having accidents outside the tray), weight loss despite maintained or increased appetite, and in advanced cases a characteristic plantigrade stance (walking on the hocks rather than on the toes).

Diabetes is diagnosed via blood and urine glucose measurement. Management involves twice-daily insulin injections and dietary modification to a high-protein, low-carbohydrate diet. Some cats, particularly those diagnosed early and managed well, achieve diabetic remission and no longer require insulin.

Chronic Kidney Disease

Chronic kidney disease (CKD) is the most common disease in older cats in the UK and is a major cause of polydipsia and polyuria. As kidney function declines, the kidneys lose the ability to concentrate urine, passing large volumes of dilute urine and triggering compensatory thirst.

Other signs of CKD include weight loss, reduced appetite, vomiting, lethargy and bad breath with an ammonia-like quality. CKD progresses gradually and is diagnosed by blood tests (creatinine, SDMA, urea) and urine specific gravity testing.

Management includes prescription kidney diets, encouraging fluid intake (wet food, water fountains, multiple water stations), phosphate binders and blood pressure management. Annual screening for cats over seven — and six-monthly for those over ten — enables earlier diagnosis when management options are most effective.

Hyperthyroidism

Hyperthyroidism — overproduction of thyroid hormone, most common in cats over ten — causes a wide range of signs including increased thirst, increased appetite with weight loss, hyperactivity or restlessness, vomiting and a deteriorating coat.

The excess thyroid hormone increases metabolic rate and can affect kidney, heart and other organ function. Diagnosis involves blood measurement of T4 (thyroid hormone). Treatment includes daily oral medication (carbimazole tablets), radioactive iodine therapy, surgical thyroidectomy, or an iodine-restricted prescription diet.

Hyperthyroidism sometimes masks concurrent CKD — once thyroid hormone levels normalise, underlying kidney disease can become apparent. This is why treatment of hyperthyroidism requires careful monitoring of kidney function alongside thyroid levels.

Other Causes of Increased Thirst

Several other conditions can cause polydipsia in cats. Pyometra (uterine infection) in entire female cats is a serious emergency presenting alongside polydipsia, lethargy, a distended abdomen and vaginal discharge. Any unspayed female cat showing these signs needs emergency veterinary care.

Hypercalcaemia (high blood calcium, sometimes associated with cancer or certain other diseases), liver disease, and some medications — particularly steroids and diuretics — can also increase water intake. Even psychological causes such as stress and boredom can occasionally result in excessive drinking.

A standard full blood count, biochemistry panel and urinalysis are the typical starting point for investigating polydipsia in cats. Based on these results, further investigation (imaging, hormone testing, urine culture) may be recommended.

Find a Vet Near You

Increased thirst in a cat warrants a vet appointment — the sooner the cause is identified, the better the outcome for most underlying conditions. Use CompareMyVet at app.comparemyvet.uk to find and compare vet practices near you and understand local consultation and blood test costs.