Cat water intake: what a change in thirst really means

Quick answer

Most of a wet-fed cat's water arrives in the bowl it eats from. That is why watching the water bowl tells you nothing until you know what the cat is eating.

A change in how much your cat drinks is one of the earliest signals you get of kidney disease, an overactive thyroid or diabetes, and it usually appears months before the cat looks ill.

There is no single number of millilitres per kilogram that tells you whether a cat is drinking too much. Total water requirement depends on how much moisture is in the food, and wet and dry diets differ enormously. What matters is the change from this cat's own normal.

• Wet food is typically around three-quarters water. Dry food is usually under a tenth. Check the labels.
• A cat that switches from wet to dry will visibly drink much more, and nothing is wrong.
• Measure properly by weighing the bowl over 24 hours, with a second bowl the cat cannot reach as an evaporation control.
• Drinking more and urinating more is different from straining in the tray and producing little. The second is an emergency.
• Any persistent increase in thirst in a cat over about seven years old deserves a blood and urine test, not a wait.

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A cat squatting repeatedly and producing little or no urine is a blocked bladder until proven otherwise, and it is a same-hour emergency.

Owners frequently read frequent tray visits as "drinking a lot". They are opposite problems. A cat that produces large puddles is polyuric. A cat that strains, cries, visits the tray again and again and produces a few drops or nothing is obstructed. This is far more common in males, kills within a day or two, and gets worse in the hours people spend waiting to see. If in doubt, look at the litter: no clump, or a tiny one, plus straining, means go now.
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Decide in 60 seconds

Why there is no millilitres-per-kilogram answer

A cat's total water requirement is met from three sources: water it drinks, water in its food, and a small amount produced by metabolism.

The proportions shift completely with diet. Wet food is mostly water, so a wet-fed cat gets the bulk of its intake at mealtimes and may visit the bowl rarely. Dry food contains very little, so a dry-fed cat has to make up almost the entire difference by drinking.

This is why per-kilogram figures circulating online cause so much confusion. Published water requirements describe total intake from all sources, for research purposes. Applied to a water bowl, they produce nonsense: a healthy wet-fed cat looks alarmingly under-hydrated, and a healthy dry-fed cat looks polydipsic.

The useful comparison is always the same cat against itself. Establish what normal looks like while your cat is well, on the diet it is actually eating, and treat a sustained departure from that as the signal.

Cats also start from a disadvantage. Their ancestors were desert animals that got their water from prey and concentrated their urine heavily. The thirst drive that follows from that is modest, which is why a cat losing water through diseased kidneys will drink more but often not enough, and why dehydration develops alongside obvious polydipsia.

Measuring it properly

The same scale does the job. Weigh the water bowl at the start and end of a 24-hour period, and the difference in grams is the intake in millilitres.

The method.

Fill the bowl and weigh it. Note the time. Twenty-four hours later, weigh it again without topping it up. The difference in grams is the millilitres consumed.

The evaporation control.

Put an identical bowl with the same amount of water somewhere the cat cannot reach, in the same room. Weigh it at the same two times. Whatever it lost is evaporation, and you subtract that from your first figure. In a warm room, or with a shallow wide bowl, evaporation is large enough to change your conclusion completely.

Multiple bowls.

Weigh all of them, including anything the cat drinks from that you did not intend, such as a glass by the bed or a dripping tap. If the cat uses a fountain, this method will not work well, and you may need to measure output instead.

Multi-cat homes.

You cannot attribute intake without separating the cats for the measurement period or watching on camera. Separating one cat for 24 hours with its own food, water and tray is a reasonable and much more informative option than guessing.

Measuring output instead.

Sometimes easier. Use a clean tray, the same litter, and count and weigh the urine clumps over 24 hours. A steady increase in the number or the size of clumps is real information, and it is often what an owner notices first.

Repeat it.

One day is a snapshot. Two or three separated days give you a range and stop a single hot afternoon from misleading you.

Drinking more: what it means

Increased thirst that is not explained by a diet change, hot weather or lactation is a symptom, not a habit. In almost all cases the cat is drinking more because it is losing more, and the kidney is where that happens.

Chronic kidney disease. The most common cause in older cats. Failing kidneys lose the ability to concentrate urine, so water is lost and thirst rises to compensate. Look for weight loss, a coat that has become unkempt, reduced appetite, occasional vomiting, and a cat that seems to have quietly aged.

Hyperthyroidism. Also an older cat disease. The giveaway combination is a huge appetite with weight loss, often with restlessness, a louder voice, an unkempt coat, a rapid heart rate and sometimes diarrhoea. The vet may feel an enlarged thyroid in the neck.

Diabetes mellitus. Often, though not always, a cat that has been overweight. Ravenous, losing weight, drinking heavily, producing large sticky urine clumps. In more advanced cases the hind legs drop so that the cat walks on its hocks, which is a nerve complication and a strong clue.

High blood calcium. Less familiar to owners but a recognised feline problem, sometimes idiopathic and sometimes associated with lymphoma. Constipation, vomiting and weight loss commonly accompany it.

Liver disease and, in unspayed females, pyometra, which is less common in cats than dogs but does occur, and comes with a sick cat and often a discharge.

Medication. Corticosteroids and diuretics both increase thirst and urination. Check what the cat is on.

Benign explanations. A recent switch from wet to dry food, hot weather, a new fountain that the cat finds interesting, a lactating queen, and a cat that has started eating more salt-rich treats.

Drinking less: what it means

Reduced drinking matters most when it is not explained by a move onto wet food.

A painful mouth. Cats with tooth resorption, periodontal disease, stomatitis or an oral tumour approach water, hesitate, and back away, or drink in a strange lopsided way. Dental pain in cats is enormously under-recognised because they carry on eating for a long time.

Nausea. A cat with kidney disease, pancreatitis or an obstruction can be dehydrated and simultaneously have no interest in drinking, because it feels sick.

The bowl. Cats dislike their whiskers brushing the sides of a narrow deep bowl, dislike water next to their food, and strongly dislike water next to the litter tray. Plastic bowls hold odour and develop biofilm. Water that has stood all day tastes different to the cat than it does to you.

The route. A bowl that can only be reached by passing the dog, the other cat, or a noisy appliance may simply not be used.

Illness generally. A cat that has stopped both eating and drinking is more urgent than one that has stopped eating alone, because dehydration is now added to whatever the underlying problem is.

Judging dehydration at home, and why the usual test fails

Pinching the skin over the shoulders and watching how fast it falls back is the test everyone knows, and it is unreliable in exactly the cats who need it most.

The tent test measures skin elasticity as well as hydration. A thin or elderly cat has lost subcutaneous fat and skin elasticity, so the skin stays tented in a perfectly hydrated animal. An obese cat's skin snaps back even when it is dehydrated.

Better indicators:

Gums. Should be moist and slippery. Tacky or dry gums are meaningful.

Eyes. Sunken eyes in a previously normal cat.

Extremities. Cool ears and paws in a flat cat suggest poor circulation and need urgent advice.

Litter output. Reduced urine production in a cat that is not drinking.

Weight. The most sensitive of all. A litre of fluid weighs a kilogram, so short-term weight changes in a cat that has not changed its food are mostly water. Weighing a sick cat daily on the same scale tells you more than any pinch test.

What the vet will want, and what they will test

Bowl and tray are two halves of the same measurement. What goes in and what comes out are both worth recording before the appointment.

Bring a urine sample if you can. Urine concentration is the first thing the vet wants, and it reframes everything. A cat that is drinking heavily and still producing concentrated urine is a very different case from one producing dilute urine. Collect fresh urine using non-absorbent litter, keep it cool, and get it to the practice quickly.

Expect blood tests covering kidney values, glucose and thyroid hormone, a urine specific gravity and dipstick, often a urine culture, and blood pressure measurement, because high blood pressure travels with both kidney disease and hyperthyroidism and damages the eyes silently.

Helping a cat drink more, when that is the goal

For cats with kidney disease, urinary crystals or a history of urethral obstruction, increasing water intake is a genuine treatment goal.

What never to do

Never restrict water because a cat is urinating in the house or in large volumes. Restricting water in a polyuric cat produces dehydration on top of the original disease, and it is the single most dangerous mistake in this area.

Never assume increased thirst is normal ageing. It is one of the most reliable early signals of treatable disease, and treating kidney disease and hyperthyroidism early materially changes outcomes.

Never give a cat human electrolyte drinks or sports drinks. Sugar and salt loads are the wrong answer, and a cat that needs fluids needs them under veterinary direction.

Never delay for a male cat straining in the tray. See the warning at the top.

Never wait to see whether the appetite recovers in a cat that is drinking nothing. Cats that stop eating are also at risk of hepatic lipidosis, and combining that with dehydration is a bad place to start treatment from.

Never rely on the skin pinch alone. Use gums, output and weight instead.

When to get help

The realistic aim: a stable weight, a steady intake you have actually measured, and a change you notice in the first weeks rather than the sixth month.

Go immediately for a cat straining in the tray with little or no urine, crying while trying to urinate, vomiting with collapse, or any cat that is flat with cold ears and paws.

Contact the practice within the week for a sustained increase or decrease in drinking that is not explained by a diet change, for increased thirst with weight loss in an older cat, for a ravenous appetite with weight loss, for larger or more frequent urine clumps, or for a cat that hesitates at the water bowl.

Book a routine senior check with blood and urine testing for any cat over about seven years old, whether or not you have noticed anything. Kidney disease, hyperthyroidism and diabetes are all commoner with age, all present first through thirst and urine, and all respond far better when they are found by a test than when they are found by a crisis.