This Symptom Needs a Vet Visit
Increased thirst in cats is not a behavioral quirk or a harmless change — it is almost always a sign that the body is compensating for a medical condition causing fluid loss. The three most common causes (kidney disease, diabetes, and hyperthyroidism) are all manageable when diagnosed early, but they worsen significantly without treatment. Do not wait weeks to see if the drinking normalizes on its own. A basic blood panel and urinalysis can identify the cause quickly.
How Much Is Too Much?
A typical 10-pound (4.5 kg) cat should drink roughly 7 to 9 ounces (200-270 ml) of water per day, including moisture from wet food. Cats eating wet food exclusively may drink very little visible water because their food is about 80 percent moisture. Cats on dry food drink more because kibble is only about 10 percent moisture.
The clinical threshold for polydipsia in cats is water intake exceeding 45 ml per kilogram of body weight per day. But you do not need to measure precisely. If you notice that your cat is:
- Visiting the water bowl much more frequently than before
- Emptying a bowl that used to last all day
- Seeking water from faucets, toilets, plant saucers, or glasses they previously ignored
- Producing significantly larger or more frequent urine clumps in the litter box
...then something has changed and it is worth investigating.
The Three Most Common Causes
Chronic Kidney Disease (CKD)
Kidney disease is the most common cause of increased thirst in cats over age seven. The kidneys' job is to concentrate urine by reabsorbing water. When kidney function declines, the kidneys lose this ability and produce dilute, watery urine in larger quantities. The cat drinks more to compensate for the increased water loss.
CKD is extremely common in older cats — studies suggest that up to 30 to 40 percent of cats over age 10 have some degree of kidney disease. It is a progressive condition, but with early diagnosis and management (dietary changes, fluid supplementation, medications to protect remaining kidney function), many cats live comfortably for years after diagnosis.
Other signs of CKD include weight loss, decreased appetite, vomiting, lethargy, and poor coat quality. But increased thirst and urination are often the first noticeable signs.
Diabetes Mellitus
Just like in humans, diabetes in cats means the body cannot properly regulate blood sugar. In Type 2 diabetes (the most common form in cats), cells become resistant to insulin, and blood sugar rises. The kidneys try to flush out the excess glucose by producing more urine, which leads to dehydration and increased thirst.
Diabetic cats are often overweight and middle-aged or older. Along with increased drinking and urination, you may notice increased appetite combined with weight loss — the cat is eating more but losing weight because their body cannot properly use the calories. Some diabetic cats develop a characteristic plantigrade stance, walking flat on their hocks rather than on their toes, due to diabetic neuropathy.
The encouraging news is that feline diabetes can sometimes be reversed. With early aggressive treatment (insulin injections and a high-protein, low-carbohydrate diet), some cats achieve diabetic remission and no longer need insulin. This makes early diagnosis particularly valuable.
Hyperthyroidism
Hyperthyroidism occurs when the thyroid gland produces too much thyroid hormone, revving up the cat's metabolism. It is the most common endocrine disorder in cats over age eight, affecting about 10 percent of senior cats.
The excess thyroid hormone increases metabolic rate across the board, leading to increased appetite with weight loss, increased thirst and urination, hyperactivity or restlessness, vomiting, and sometimes a rapid heart rate. You might notice your older cat acting like a kitten again — more active, more vocal, seemingly hungry all the time — while paradoxically losing weight.
Hyperthyroidism is very treatable. Options include daily oral medication (methimazole), radioactive iodine therapy (which is curative), surgical removal of the affected thyroid tissue, or a prescription iodine-restricted diet.
Other Possible Causes
Urinary tract infection. UTIs can increase thirst and urination, though they are less common in cats than in dogs. If the increased drinking is accompanied by straining to urinate, bloody urine, or urinating outside the litter box, a UTI is possible.
Liver disease. The liver plays a role in water balance, and liver dysfunction can cause increased thirst. This is less common than kidney disease and usually presents with other symptoms (jaundice, poor appetite, lethargy).
Medications. Corticosteroids (like prednisolone) cause increased thirst and urination as a predictable side effect. If your cat recently started a new medication, check with your vet.
Diet change. Switching from wet food to dry food can cause a noticeable increase in water consumption that is normal and expected — the cat is simply compensating for the reduced moisture in their diet. This is not a medical concern.
Hot weather. Cats drink more in warm weather. If the increase coincides with a heat wave and the cat is otherwise acting normally, it may simply be temperature-related. But if it persists beyond the warm spell, investigate further.
What the Vet Will Do
Diagnosing the cause of increased thirst is usually straightforward. The vet will likely run:
- Complete blood count (CBC) — checks for infection, anemia, and blood cell abnormalities
- Blood chemistry panel — measures kidney values (BUN, creatinine, SDMA), blood glucose, liver enzymes, and electrolytes
- Total T4 (thyroid hormone level) — screens for hyperthyroidism
- Urinalysis — assesses urine concentration, checks for glucose, protein, bacteria, and crystals
These tests together paint a clear picture and usually identify the cause in one visit. Treatment can often begin immediately.
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Written by David Park
David writes about science and the natural world. He enjoys turning research findings into interesting, easy-to-understand articles.