Cat drinking a lot of water: common causes and what to do

Reading time 6 min · Level 1: Why the symptom appears

The short answer: A cat that starts drinking more than usual nearly always does so because it is passing more urine, and the body is trying to replace the lost fluid. Sometimes there is a simple explanation, such as a switch from wet to dry food or a hot summer. In an adult or older cat the three most common medical causes are chronic kidney disease, diabetes and an overactive thyroid. All three show up in a blood and urine test. Measure how much your cat drinks over 24 hours, bring a urine sample if you can and book a vet appointment, even if the cat otherwise seems well.

How much should a cat drink?

Less than most people think. Cats descend from desert animals and are built to get most of their fluid from food and to concentrate their urine rather than drink. AniCura states that a cat normally takes in 20 to 50 ml of fluid per kilo of body weight per day, including the water in its food¹. FirstVet draws the line at 100 ml per kilo per day: if the cat drinks more than that, something is not right². For a 4 kg cat, that means more than 400 ml of water a day is too much.

Diet makes a big difference. A cat that eats only dry food drinks more from the bowl than a cat on wet food, because dry food contains almost no water¹. If you have recently changed food, that may explain some of it. What should make you react is a change: the cat drinking clearly more than it used to, with nothing else having changed.

How to measure at home

It is hard to see how much a cat drinks, especially if it goes outdoors. Evidensia suggests a simple method: pour one litre of water into the bowl, do not top it up, and measure what is left after 24 hours³. Repeat for two or three days and write the figures down. With several cats or bowls in several places the measurement is less reliable, but a clear increase usually shows in how often you refill.

Look at the litter tray too. Bigger and more frequent urine clumps are the same thing seen from the other end. A urine sample from home makes the vet visit more efficient. Swap the litter for clean, unpopped popcorn kernels, and the urine collects at the bottom and can be poured into a clean jar³.

The three most common medical causes

1. Chronic kidney disease. One of the most common diagnoses in older cats, and usually a slowly progressive disease⁴. The kidneys lose their ability to concentrate urine, so the cat passes more water and has to drink to keep up. Over time it may lose appetite and weight and sometimes vomit³. The increased thirst is often the first thing owners notice, and it creeps in so gradually that it is easily put down to age. What the test results mean, including creatinine, SDMA and staging, is covered in our article on high kidney values in cats.

2. Diabetes. Most common in middle-aged and older cats, and according to the International Society of Feline Medicine (ISFM) it appears to be becoming more common⁵. When blood sugar is too high, sugar spills into the urine and pulls water with it. The typical pattern is a cat that drinks and urinates more, eats more than before and still loses weight³. Being overweight raises the risk, and getting the weight down is part of treatment⁵.

3. Overactive thyroid. Known as hyperthyroidism, it is the most common hormonal disease in older cats³. The cat often becomes restless and hungry, loses weight despite a good appetite, gets a scruffier coat and drinks more. Today the disease is often found on a blood test long before the cat looks obviously ill, because thyroid hormone is included in many senior health checks⁶. The thyroid and the kidneys are linked: raised kidney values can appear only after the thyroid has been treated. That is one reason the vet keeps an eye on both⁶.

Other causes your vet will consider

Urinary tract infection is more common in cats that already have kidney disease or diabetes. Liver disease, womb infection in unspayed females and some tumours can also cause increased thirst. Medicines can raise thirst as a side effect too¹. Tell your vet which medicines the cat takes or has recently had, including any given as an injection at the clinic.

The work-up usually follows the same order. The vet asks how it started, examines the cat, takes blood and urine samples and often measures blood pressure⁴. Urine concentration says a lot at once: dilute urine in a cat that drinks a lot confirms that the thirst is real. Sometimes ultrasound or X-rays are needed to get further³.

When to see the vet

The same day or as an emergency if the cat drinks a lot and also stops eating, vomits repeatedly, is lethargic or seems dehydrated. A diabetic cat can become seriously ill quickly, and so can a cat with advanced kidney disease. It is also an emergency if a cat, especially a male, keeps going back to the litter tray and straining without passing urine. That is not the same as urinating a lot and can become life-threatening within a short time.

Within a few days if the cat drinks or urinates more than usual but otherwise eats and behaves normally. Both AniCura and Evidensia make it clear that your own impression of increased thirst is reason enough for an examination¹³. The earlier kidney disease, diabetes or a thyroid problem is found, the more treatment options there are.

What you can do yourself

Keep water available. It may seem logical to ration water when the cat urinates a lot, but that is the wrong way round. A cat drinking to replace lost fluid will become dehydrated if it is not allowed to drink³.

Measure, weigh and take notes. Water per day, weight, appetite and whether anything has changed in the food or routine. It takes five minutes and saves time at the vet.

Do not change the food before the visit. A new food makes both thirst and test results harder to interpret. Special diets, such as a kidney diet, are chosen by the vet based on the diagnosis.

Book a health check even when all seems well. Many of these diseases start quietly. An older cat that has regular blood and urine tests often gets help before the thirst becomes noticeable.

Frequently asked questions

Why is my old cat drinking so much?

In older cats, chronic kidney disease, diabetes and an overactive thyroid are the most common explanations. None of them can be told apart at home. A blood and urine test gives the answer, and it is worth doing even if the cat otherwise seems fine.

Can dry food make a cat drink more?

Yes. Dry food contains almost no water, so a cat on dry food alone drinks more from the bowl than a cat on wet food. That explains a steady, high level, but not an increase that appears without any change of food.

How much water is too much for a cat?

FirstVet states that more than 100 ml of water per kilo of body weight per day is abnormal². For a 4 kg cat that is 400 ml. Measure over a couple of days before drawing conclusions.

Should I give my cat less water if it urinates a lot?

No. The cat drinks to replace fluid it has already lost. Restricting water risks dehydration. Keep the water out and let your vet find out why.

That was the short answer. If you have a question about your own pet, email us at info@herbiovet.se. We reply within one working day.