Why Is My Cat Drinking a Lot of Water? Causes & When to See a Vet

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Increased thirst in cats, known medically as polydipsia, is one of those symptoms that owners often dismiss or fail to notice until it becomes extreme. Unlike dogs, who drink noisily and frequently, cats are naturally low-thirst animals descended from desert ancestors who obtained most of their water from prey. A cat drinking significantly more water than usual is a red flag for several serious underlying conditions, and it should never be ignored.

In my practice, I've diagnosed countless cases of kidney disease, diabetes, and hyperthyroidism purely because an owner noticed their cat suddenly emptying the water bowl every day or drinking from taps and toilets. The challenge is knowing what "too much" actually looks like, because the baseline varies between cats.

This guide covers everything you need to know about increased thirst in cats, what causes it, and when you need to see your vet.

How Much Water Should a Cat Drink?

A healthy adult cat typically drinks around 40-60ml of water per kilogram of body weight per day. For a 4kg cat, that's roughly 160-240ml daily. Cats on wet food diets drink less than cats on dry food, as wet food contains around 70-80% moisture.

Polydipsia is defined as drinking more than 100ml per kilogram per day. For a 4kg cat, that's anything over 400ml of water daily which is significantly above normal.

The problem is that most owners don't measure their cat's water intake. The easiest way to notice increased drinking is a change in behaviour: your cat suddenly starts drinking from the tap, hovering around the water bowl constantly, or drinking from unusual places like the bath, sink, or even the toilet.

Why Is My Cat Drinking So Much Water?

1. Chronic Kidney Disease (CKD)

Kidney disease is one of the most common causes of increased thirst in cats, particularly in older animals. As the kidneys lose their ability to concentrate urine effectively, the cat produces large volumes of dilute urine and must drink more to compensate. Other signs include weight loss, reduced appetite, vomiting, and a dull coat. Early detection through blood and urine testing is critical for managing CKD effectively.

2. Diabetes Mellitus

Diabetes occurs when the pancreas doesn't produce enough insulin or the body can't use it effectively, leading to high blood glucose levels. Excess glucose spills into the urine, dragging water with it and causing excessive urination (polyuria) and compensatory thirst. Other signs include increased appetite with weight loss, lethargy, and a poor coat. Diabetes is more common in overweight male cats.

3. Hyperthyroidism

An overactive thyroid gland is extremely common in middle-aged and older cats and causes a ramped-up metabolism. Increased thirst is one of several symptoms, alongside weight loss despite good appetite, hyperactivity, vomiting, diarrhoea, and a scruffy coat. It's easily diagnosed with a blood test and very manageable once treated. For a complete guide, read our article on hyperthyroidism symptoms in cats.

4. Liver Disease

Hepatic disease can cause polydipsia, particularly in cases of hepatic lipidosis (fatty liver disease) or cholangiohepatitis. Other signs include jaundice (yellow gums and eyes), vomiting, lethargy, and reduced appetite.

5. Urinary Tract Infection or Lower Urinary Tract Disease

Cats with UTIs or feline lower urinary tract disease (FLUTD) sometimes drink more water in an attempt to flush the system. This is usually accompanied by frequent trips to the litter tray, straining, blood in the urine, or urinating outside the tray. For more on urinary symptoms, see our guide on cat UTI symptoms.

6. Pyometra (in Unspayed Female Cats)

Pyometra is a life-threatening infection of the uterus that occurs in unspayed female cats. Increased thirst and urination are early signs, alongside lethargy, vaginal discharge, vomiting, and a distended abdomen. This is a surgical emergency.

7. Medications

Certain medications, particularly corticosteroids (prednisolone) and diuretics, cause increased thirst as a side effect. If your cat has recently started medication and is drinking more, mention this to your vet.

8. Diet Change

Switching from wet food to dry food will naturally increase water intake, as dry food contains only around 10% moisture. Increased salt or protein in the diet can also drive thirst. This is usually obvious from the timeline and not a cause for concern.

9. Hot Weather or Increased Activity

Cats drink more in warm weather or after increased activity. This is normal and temporary. If the increase in drinking persists beyond a few days or there are other symptoms, investigate further.

10. Stress

Some cats drink more when anxious or stressed, though this is less common than other causes. It's usually accompanied by other behavioural changes like hiding, over-grooming, or litter tray issues.

Other Symptoms to Watch For

Increased thirst rarely occurs in isolation. Look for:

• Increased urination: Larger clumps in the litter tray, needing to empty the tray more often
• Weight loss: Despite normal or increased appetite
• Vomiting: Particularly first thing in the morning
• Reduced appetite or fussiness: See our guide on why cats stop eating
• Lethargy or behaviour changes
• Changes in coat quality: Dull, greasy, or unkempt
• Bad breath: Particularly a chemical or ammonia smell

For a full guide to recognising illness in cats, read our overview of cat illness symptoms and when to act.

When Should I See the Vet?

You should book a vet appointment if your cat:

• Has been drinking noticeably more water for more than a few days
• Is urinating significantly more than usual
• Is showing any other symptoms: weight loss, vomiting, lethargy, appetite changes
• Is an older cat (over 7 years): they're at higher risk of kidney disease, diabetes, and hyperthyroidism
• Is drinking excessively and also seems unwell: contact your vet the same day

Early diagnosis of conditions like kidney disease, diabetes, and hyperthyroidism significantly improves outcomes. Don't wait for symptoms to worsen.

How Is Increased Thirst Diagnosed?

Your vet will start with a full clinical examination and detailed history. They'll then typically recommend:

• Blood tests: To check kidney function, blood glucose, thyroid hormones, liver enzymes, and electrolytes
• Urinalysis: To measure urine concentration, check for glucose, protein, blood, and signs of infection
• Blood pressure measurement: High blood pressure is common with kidney disease and hyperthyroidism
• Imaging (ultrasound or X-ray): If indicated, to assess kidneys, bladder, liver, and other organs

In many cases, a combination of blood and urine testing will identify the cause straight away.

How Litter Sense Can Help Detect Problems Early

Several of the conditions that cause increased thirst, particularly kidney disease, diabetes, and urinary tract disease, also produce changes in the urine that Litter Sense can detect. By monitoring your cat's urine daily, Litter Sense can flag early warning signs before you even notice increased drinking, giving you the chance to act early when treatment is most effective.

To understand more about how this works, read our complete guide on how Litter Sense monitors cat health.

Frequently Asked Questions

How much water is too much for a cat?

As a rough guide, a cat drinking more than 100ml per kilogram of body weight per day is drinking too much. For a 4kg cat, that's over 400ml daily. The easiest way to monitor is by observing behaviour: if your cat is suddenly constantly at the water bowl, drinking from taps, or emptying the bowl daily when they didn't before, that's too much.

Should I limit my cat's water if they're drinking too much?

No. Never restrict water. If your cat is drinking excessively, it's because their body needs it (usually due to increased urination). Restricting water will cause dehydration and worsen the underlying condition. Instead, see your vet to identify and treat the cause.

Can a cat drinking too much water be an emergency?

Increased thirst itself is not usually an emergency, but the underlying cause can be. If your cat is drinking excessively and also vomiting, lethargic, not eating, or seems unwell, contact your vet the same day.

Why is my cat drinking water but not eating?

A cat that drinks more but eats less may have kidney disease, liver disease, or another metabolic condition. This combination of symptoms warrants a vet appointment within 24 hours.

Can dehydration cause increased thirst in cats?

Yes, but dehydration makes a cat feel unwell and lethargic, so they often don't drink enough to compensate. Increased thirst usually indicates a condition causing excessive urination (kidney disease, diabetes) rather than simple dehydration.

Is it normal for older cats to drink more water?

No. While kidney disease, diabetes, and hyperthyroidism are more common in older cats, age itself is not a cause of increased thirst. Any senior cat drinking noticeably more should be checked by a vet.