Why Is My Cat Drinking So Much Water?
A sudden increase in water intake is one of the most reliable early warning signs of illness in cats. Here are the 10 most common causes, how much cats should normally drink, and exactly when to see a vet.
Polydipsia — the medical term for excessive drinking — is one of the most clinically significant symptoms a cat can show, because it reliably indicates that the body is either losing more fluid than normal or the kidneys are unable to concentrate urine. Unlike many cat symptoms that are vague or easily mistaken for behavioural change, polydipsia has a relatively short list of causes — almost all of which are diagnosable with a straightforward blood and urine test. This makes it one of the most actionable symptoms an owner can bring to their vet.
How Much Water Should a Cat Normally Drink?
A healthy adult cat typically drinks 30–60 ml of water per kilogram of body weight per day. For a 4 kg cat, this is approximately 120–240 ml daily — roughly half to one standard cup. However, water intake varies significantly based on diet: cats fed exclusively wet food get most of their water from their food and may drink very little from a bowl; cats on a dry-only diet must compensate by drinking more from a bowl. A cat on dry food drinking the equivalent of 1–2 cups daily is not unusual. The key indicator is a change from your individual cat's baseline — not a comparison to an average.
How to Measure Your Cat's Water Intake
- 1Use a measuring jug to fill your cat's water bowl with a known amount (e.g. 400 ml) each morning
- 2At the same time the next morning, measure what remains in the bowl
- 3Subtract the remainder from the starting amount to get the approximate daily intake
- 4Do this for 3 consecutive days to get an average — intake varies day to day
- 5If you have multiple cats sharing a bowl, this method cannot distinguish individual intake — separate bowls are needed for accurate measurement
- 6Concern threshold: more than 100 ml/kg/day is a reliable indicator of polydipsia warranting veterinary investigation in most cats
🚨 See Your Vet Urgently If Increased Drinking Is Accompanied By:
- •Not eating or eating significantly less than usual for more than 24 hours
- •Vomiting — especially repeated vomiting or vomiting combined with lethargy
- •Rapid or labored breathing
- •Extreme lethargy — difficulty rising, unresponsive, or very weak
- •Weight loss that has been happening over weeks to months
- •Yellow tinge to the gums, skin, or whites of the eyes (jaundice)
- •Straining to urinate or producing no urine (especially male cats — urethral blockage is a life-threatening emergency)
- •Blood in urine
- •Seizures or sudden disorientation
- •Your cat has diabetes and is vomiting — this can indicate diabetic ketoacidosis, which is an emergency
10 Common Causes of Excessive Thirst in Cats
These causes are organized from most common in middle-aged and senior cats (where most polydipsia cases originate) to less common causes. Kidney disease, hyperthyroidism, and diabetes account for the vast majority of polydipsia cases in cats over 7 years old.
Chronic Kidney Disease (CKD) — Most Common in Senior Cats
CriticalCKD is the most common cause of polydipsia in cats, and is extremely prevalent — studies suggest up to 30–40% of cats over 10 years develop some degree of kidney disease. Damaged kidneys lose their ability to concentrate urine, so water passes through without being retained. The cat drinks more to compensate for the water lost in large volumes of dilute urine. Other classic signs: weight loss despite normal appetite, reduced appetite in later stages, occasional vomiting (particularly in the morning), lethargy, and bad breath with an ammonia-like odor. CKD is progressive but manageable — early detection dramatically improves outcomes. Annual blood and urine panels from age 7 are the best preventive strategy.
Symptoms:
Increased thirst and urination, weight loss, reduced appetite, vomiting (especially morning), ammonia-like breath, lethargy. Develops gradually over months.
Action:
Blood test (BUN, creatinine, SDMA) and urine specific gravity. CKD is staged using IRIS guidelines. Management: kidney-specific diet, hydration support, phosphorus binders, anti-nausea medication, blood pressure management.
Hyperthyroidism — Most Common Endocrine Disease in Older Cats
CriticalAn overactive thyroid gland is the most common hormonal disease in cats over 10 years and one of the top three causes of polydipsia in older cats. Excess thyroid hormone accelerates metabolism dramatically — including kidney filtration rate and gut motility. The result is increased thirst, increased urination, increased appetite (often ravenous despite weight loss), hyperactivity, and vomiting or diarrhea. Hyperthyroidism also causes secondary hypertension (high blood pressure) which, untreated, damages the eyes, kidneys, heart, and brain. It is highly treatable — early diagnosis prevents this secondary damage.
Symptoms:
Increased thirst and urination, weight loss despite ravenous appetite, hyperactivity and restlessness, vomiting, diarrhea, poor coat quality, rapid heart rate, possible heart murmur.
Action:
Blood test for T4 (thyroid hormone). Treatment: daily antithyroid medication (methimazole/carbimazole), radioactive iodine therapy (curative, gold standard), prescription iodine-restricted diet, or surgical thyroidectomy.
Diabetes Mellitus
CriticalFeline diabetes occurs when the pancreas cannot produce sufficient insulin or cells become resistant to it, causing glucose to accumulate in the bloodstream. When blood glucose exceeds the kidney's reabsorption threshold (renal threshold), glucose spills into the urine — and because glucose is osmotically active, it draws water with it, causing large volumes of glucose-containing urine and compensatory polydipsia. Classic presentation: polydipsia combined with polyuria (increased urination), weight loss despite increased appetite, and a plantigrade stance (walking on hocks/heels rather than toes, caused by diabetic neuropathy). Feline diabetes is particularly interesting because some cats can achieve diabetic remission with early, aggressive insulin therapy and a low-carbohydrate diet.
Symptoms:
Increased thirst and urination, weight loss despite increased appetite, sweet or fruity odor to breath or urine, walking flat on hocks (plantigrade stance), lethargy, poor coat.
Action:
Blood glucose (fasting and repeated — stress hyperglycaemia in cats makes single readings unreliable) and fructosamine. Urine for glucose and ketones. Insulin therapy and dietary management (high-protein, low-carbohydrate diet strongly associated with remission).
Liver Disease
High priorityHepatic disease — including hepatic lipidosis (fatty liver disease), inflammatory liver disease (cholangitis), and hepatic lymphoma — can cause polydipsia through several mechanisms including impaired production of proteins that regulate fluid balance and accumulation of toxins normally cleared by the liver. Cats with liver disease often show jaundice (yellow tinge to the gums, eyes, and skin), which distinguishes it from other causes of polydipsia.
Symptoms:
Increased thirst, jaundice (yellow gums/eyes), reduced appetite, vomiting, weight loss, lethargy, possible pot-bellied appearance (ascites).
Action:
Blood tests (liver enzymes, bilirubin, bile acids). Ultrasound. Treatment depends on the specific liver condition.
Pyometra (Intact Female Cats)
CriticalPyometra — infection of the uterus — is a life-threatening condition affecting intact (unspayed) female cats, typically occurring weeks after a heat cycle. It causes polydipsia because bacterial toxins interfere with the kidney's ability to concentrate urine. An open pyometra (where the cervix is open) may show vaginal discharge; closed pyometra (no discharge) is more dangerous as infection builds up internally. Polydipsia combined with lethargy, reduced appetite, and abdominal distension in an intact female cat warrants emergency evaluation.
Symptoms:
Polydipsia, lethargy, reduced appetite, possible vaginal discharge (open type), abdominal enlargement. Intact female cat. Develops weeks after heat cycle.
Action:
Emergency veterinary assessment. Diagnosis by physical exam, ultrasound. Surgical spaying is the definitive treatment. Antibiotics alone are not adequate for pyometra.
Medication Side Effects
MonitorSeveral medications commonly given to cats cause polydipsia as a side effect. Corticosteroids (prednisolone, dexamethasone) are the most common cause of iatrogenic (medication-induced) polydipsia — they interfere with the antidiuretic hormone pathway, causing dilute urine and compensatory drinking. Other medications that can increase water intake: diuretics (furosemide), some anticonvulsants, and phenobarbitone. If polydipsia began after starting a new medication, this is almost certainly the cause.
Symptoms:
Increased drinking and urination beginning after starting a new medication, especially corticosteroids. Dog may also have increased appetite on steroids.
Action:
Review medication with your vet. Never stop prescribed medication without guidance — dosage adjustment or an alternative drug may resolve the issue.
Hypercalcaemia (High Blood Calcium)
High priorityElevated blood calcium interferes with the kidneys' response to antidiuretic hormone (ADH), causing polyuria and compensatory polydipsia. In cats, hypercalcaemia is most commonly caused by idiopathic hypercalcaemia (of unknown cause), lymphoma (particularly mediastinal lymphoma in young cats), or less commonly by primary hyperparathyroidism. Any cat with polydipsia, constipation, weakness, and vomiting should have calcium measured on their bloodwork.
Symptoms:
Polydipsia, weakness, lethargy, constipation, vomiting, reduced appetite. Possible weight loss.
Action:
Blood calcium level (total and ionised). Diagnosis of underlying cause requires further investigation. Treatment depends on the cause — lymphoma, idiopathic, or parathyroid disease require different approaches.
Fever or Infection
MonitorAny systemic infection or fever increases metabolic rate and fluid loss, causing increased thirst as part of the normal physiological response. This is typically acute (sudden onset with other signs of illness) rather than a gradual increase in water intake. The polydipsia resolves when the infection or fever is treated.
Symptoms:
Sudden increased drinking, fever (warm to touch, ears hot), lethargy, reduced appetite, possible other signs of infection source (respiratory, wound, urinary).
Action:
Veterinary examination including temperature. Blood and urine tests if infection source is not obvious. Antibiotic therapy for bacterial infections.
Dietary Causes — Dry Food Only Diet or Salty Treats
Low riskCats eating exclusively dry food must drink significantly more water to compensate for the low moisture content of kibble (dry food contains approximately 8–10% water versus 75–80% in wet food). A cat recently switched from wet to dry food will show a noticeably increased interest in water — this is physiologically normal and not a disease. Similarly, salty treats or high-sodium foods will transiently increase thirst. If diet is the cause, the increased drinking should be consistent and proportionate, with no other symptoms and no change in body weight.
Symptoms:
Increased drinking coinciding with switch to dry food or high-sodium treats. Otherwise healthy cat — good body weight, normal activity, eating well.
Action:
Add wet food to the diet or switch to a mixed wet/dry diet. The water intake should normalise. A water fountain often significantly increases water consumption in cats who drink inadequately on dry food.
Heat and Environmental Factors
Low riskCats in hot environments, particularly in summer or in houses without air conditioning, will drink more to regulate body temperature. This is physiologically normal — the same mechanism as humans sweating. Activity level also affects water intake. If the increased drinking is clearly seasonal, correlates with temperature, and the cat is otherwise healthy, this is likely environmental rather than medical.
Symptoms:
Increased water intake in summer months or hot conditions, otherwise healthy cat with no other symptoms, resolves in cooler weather.
Action:
Ensure multiple water sources in cool areas of the home. A ceramic or stainless steel water bowl stays cooler than plastic. Consider a cat water fountain — the moving water encourages drinking and stays cooler.
Polydipsia & Polyuria — Why They Always Come Together
In almost every case, polydipsia (excessive drinking) and polyuria (excessive urination) occur simultaneously — PU/PD as vets call them. This is because in most causes, the kidneys either cannot concentrate urine (kidney disease, diabetes insipidus) or glucose/other substances draw water into the urine (diabetes mellitus), resulting in large volumes of dilute urine. The cat then drinks more to replace the fluid lost. Owners often notice the litter box changes first: larger, heavier clumps, more frequent litter box trips, or accidents outside the box. These litter box changes are often an earlier and more obvious sign of PU/PD than watching the water bowl.
What Your Vet Will Test
| Test | What it checks |
|---|---|
| Blood biochemistry panel | Kidney values (BUN, creatinine, SDMA), liver enzymes, blood glucose, calcium, thyroid hormone (T4), electrolytes |
| Complete blood count (CBC) | Red and white blood cell counts — anaemia is common in CKD; infection signs in pyometra or systemic disease |
| Urinalysis | Urine specific gravity (concentration — the most important test in polydipsia), glucose in urine, protein, blood, bacteria, casts |
| Urine culture | Bacterial infection in urine — important in cats with any urinary symptoms alongside polydipsia |
| Blood pressure measurement | Hypertension is common in CKD and hyperthyroidism — and accelerates organ damage if untreated |
| Abdominal ultrasound | Kidney size and structure, liver, adrenal glands, uterus in intact females, abdominal lymph nodes |
Encouraging Your Cat to Drink More Water
Regardless of the underlying cause, adequate hydration supports kidney function and overall health in cats. Strategies to increase water intake: place multiple water bowls in different locations (cats often prefer drinking away from their food); use a cat water fountain — moving water is more attractive to most cats than still water; try a wide, shallow bowl — many cats dislike their whiskers touching the sides; offer wet food as part or all of the diet; add a small amount of low-sodium chicken or tuna broth to water occasionally; ensure bowls are cleaned daily — algae and biofilm buildup deters drinking; experiment with different bowl materials — some cats prefer glass or stainless steel over plastic.
Monitor Your Cat's Body Condition During Treatment
Conditions causing polydipsia — particularly kidney disease, hyperthyroidism, and diabetes — often cause gradual weight loss that can be missed until significant. PawScan's photo scan gives you an instant body condition score to track whether your cat is maintaining weight during treatment.
Scan your pet nowFrequently Asked Questions
How much water is too much for a cat to drink?▾
A useful rule of thumb: more than 100 ml per kilogram of body weight per day is considered polydipsia and warrants veterinary investigation. For a 4 kg cat, this is more than 400 ml daily. However, the most reliable approach is to notice a change from your individual cat's normal baseline rather than comparing to a number. A cat that has always drunk very little and starts frequently visiting the water bowl is worth investigating even if the absolute amount isn't extreme.
My cat is drinking more — could it just be the heat?▾
It's possible if the increase is clearly seasonal, mild, and your cat is otherwise completely normal — good weight, eating well, normal energy. However, heat is an easy explanation that can mask a genuine medical problem. If the increased drinking persists beyond the hot weather, is accompanied by any other change (weight, appetite, litter box, behavior), or your cat is over 7 years old, a veterinary check with bloodwork is strongly recommended.
Can a cat drink too much water?▾
In a strictly technical sense, primary polydipsia (compulsive drinking not driven by a physiological need) exists in cats but is exceptionally rare. In practice, if your cat is drinking a lot, the water intake is almost always secondary to a medical condition causing excessive fluid loss. The thirst is a symptom, not the problem — the underlying cause is what needs investigation.
My cat eats wet food and I've noticed they drink more recently — should I be concerned?▾
Yes — this is actually more significant than increased drinking in a cat on dry food. Cats on wet food get most of their water from their food and should drink very little from a bowl. If a wet-food cat starts noticeably visiting the water bowl, this suggests genuine polydipsia beyond what their diet requires, and warrants a veterinary check. The same concern applies to any cat showing a change from their established pattern.
How quickly can kidney disease or diabetes develop?▾
Both conditions develop gradually over months to years, which is exactly why they're often caught late — the change is slow enough to be normalized by the owner ('oh, she's always been thirsty'). This is why annual bloodwork from age 7 is so valuable — it can detect abnormalities in kidney values or blood glucose before symptoms are obvious, when treatment is most effective.
This article is for educational purposes only. Always consult a licensed veterinarian for medical advice specific to your pet.