Cat Drinking a Lot of Water: Causes and What to Do

How much water is normal for a cat?

A rough guide is that a cat needs about 50 to 60 ml of water per kilogram of body weight per day, including moisture from food. A 4 kg cat eating wet food may drink very little from the bowl because the food itself is mostly water, while a cat on dry food will drink more. International Cat Care notes that what is normal varies between individuals and diets.

This means the most useful measure is change from your cat's own baseline, not an absolute number. If you are measuring because you are concerned, use a marked water bowl, refill it with a known volume each day and record what is left. Do this for several days and take the record to your vet.

Common causes of increased drinking

PDSA lists chronic kidney disease, diabetes mellitus and hyperthyroidism as the three conditions most commonly associated with increased drinking and urination in cats. All three are more common in middle-aged and older cats, and all need blood and urine tests to diagnose.

Other causes include liver disease, infection, pancreatitis, certain medications, and less commonly, a behavioural condition called psychogenic polydipsia. Hot weather, a switch to dry food, increased activity or a salty treat can also increase drinking temporarily, but these explanations should not be assumed without ruling out medical causes.

• Chronic kidney disease: common in older cats; drinking more and urinating more, sometimes with weight loss and reduced appetite.
• Diabetes mellitus: increased drinking, urination and appetite, often with weight loss; more common in overweight cats.
• Hyperthyroidism: increased appetite, drinking, activity and vocalisation with weight loss; typically in cats over 10.
• Liver disease: may cause increased drinking, jaundice, vomiting or reduced appetite.
• Infection or fever: can increase water needs; look for lethargy or other signs of illness.
• Diet or environment: dry food, hot weather or salty treats can raise intake temporarily.

Kidney disease in older cats

Chronic kidney disease (CKD) is one of the most common diagnoses in senior cats. Cats Protection estimates that around one in three cats over 12 has some degree of CKD. The kidneys lose their ability to concentrate urine, so the cat drinks more to replace what is lost and urinates larger volumes.

CKD cannot be cured, but early diagnosis and management — including a veterinary kidney diet, regular monitoring and sometimes medication or fluids — can improve quality of life and slow progression. If your older cat is drinking more, a blood test and urine test are the first steps your vet will recommend.

Diabetes and hyperthyroidism

Diabetes mellitus in cats often presents as the classic triad of increased drinking, increased urination and increased appetite with weight loss. Overweight cats, British Shorthairs and Burmese cats appear to be at higher risk. With early diagnosis, some cats can achieve diabetic remission with insulin and dietary management.

Hyperthyroidism causes an overproduction of thyroid hormone, driving up metabolism. Affected cats may eat ravenously, drink more, be restless or vocal, have a rapid heart rate and lose weight despite a good appetite. It is usually seen in cats over 10 and is treated with medication, radioactive iodine therapy, surgery or a special prescription diet.

How your vet will investigate

Your vet will ask about the duration and pattern of drinking, diet, appetite, urination, weight, activity and any other symptoms. The examination includes body condition, hydration, heart rate, abdominal palpation and sometimes checking blood pressure.

Blood and urine tests are central to the investigation. A full blood panel checks kidney values, liver enzymes, glucose, thyroid hormone and blood cells. A urine sample helps assess concentration and rule out infection. If diabetes is suspected, your vet may also check fructosamine, which reflects average blood glucose over recent weeks.

What to do while you wait for the appointment

Do not restrict your cat's access to water. If the increased drinking is caused by kidney disease or diabetes, limiting water would be harmful. Provide fresh water in several locations, keep bowls clean and consider a water fountain if your cat prefers moving water.

Note exactly how much your cat drinks over two to three days using a marked bowl, and record appetite, urination frequency and any other changes. If your vet asks for a urine sample, use clean non-absorbent litter or an empty tray to collect it and store it in a sealed container in the fridge for up to 24 hours.