Cats normally drink 40 to 60 mL of water per kg of body weight daily — roughly a quarter to half a cup for a 10-pound cat. When water intake suddenly increases, especially in middle-aged or older cats, the cause is almost always medical: chronic kidney disease, diabetes, or hyperthyroidism account for the large majority of cases. A vet visit with bloodwork is the right next step.
Last reviewed: May 2026
What Counts as "Excessive" Thirst
Vets call increased thirst polydipsia and increased urination polyuria — together PU/PD. The clinical cutoff is more than 100 mL per kg per day, but most owners notice the change long before that. Signs include needing to refill the water bowl more often, the cat hanging around the tap, drinking from unusual sources (sinks, toilet, plant saucers), bigger urine clumps in the litter box, and urinating outside the box because the existing box is saturated. A handy home measurement: weigh the water bowl morning and evening for two days and convert grams lost (after accounting for evaporation) to mL.
The Three Most Common Causes
Chronic kidney disease (CKD) is the leading cause of PU/PD in cats over 10, affecting about 30 percent of senior cats. The kidneys lose the ability to concentrate urine, so cats produce large volumes of dilute urine and compensate by drinking more, as outlined in the IRIS CKD Staging Guidelines, 2023. Diabetes mellitus causes glucose to spill into urine, dragging water with it. Diabetic cats are usually overweight middle-aged neutered males with a recent weight loss despite normal or increased appetite. Hyperthyroidism, the most common endocrine disease in older cats, accelerates metabolism and increases thirst — affected cats typically show weight loss, increased appetite, and a hyperactive demeanor.
Less Common but Important Causes
Urinary tract infection (especially in diabetic or senior cats), high blood calcium from cancer or idiopathic hypercalcemia, liver disease, certain medications (prednisolone, furosemide), and rare conditions like diabetes insipidus all cause PU/PD. The AAFP Senior Care Guidelines, 2021 recommend bloodwork and a urinalysis at every senior wellness visit precisely because so many of these conditions present subtly.
What the Vet Will Test
Workup for new-onset PU/PD typically includes a complete blood count, chemistry panel (BUN, creatinine, glucose, calcium, phosphorus, liver enzymes, electrolytes), urinalysis (specific gravity, glucose, ketones, protein), total T4 for thyroid status, and SDMA for early kidney disease. Specific gravity less than 1.035 with appropriate hydration suggests reduced concentrating ability. Glucose in urine plus high blood glucose confirms diabetes. Elevated T4 confirms hyperthyroidism.
Treatment — Depends on the Diagnosis
CKD is managed with a kidney-specific diet, hydration support (subcutaneous fluids at home for advanced cases), phosphorus binders, and ACE inhibitors or telmisartan when proteinuria is present. Cats can live months to years with appropriately managed CKD. Diabetes is treated with twice-daily insulin (glargine or Prozinc) and a high-protein, low-carbohydrate diet — about 30 percent of cats achieve diabetic remission within the first 6 months if treatment starts early. Hyperthyroidism has four options: methimazole tablets, prescription Y/D diet, radioactive iodine therapy (curative, $1,500 to $2,500), or thyroidectomy. Most senior cats do well long-term on methimazole or radioiodine, per the AAFP-AAHA Feline Life Stage Guidelines, 2021.
How to Monitor at Home
Measure water intake weekly using the bowl-weight trick. Track urine clump size and number with each litter scoop. Note appetite, weight, and energy. Bring this log to every senior wellness visit — patterns are more informative than a single reading.
When to See a Vet
A new pattern of increased drinking lasting more than a few days deserves a workup. Don't wait for weight loss or vomiting.
Call your vet today if:
- Water intake noticeably increased for more than 3 days
- Larger or more frequent urine clumps in the litter box
- Urinating outside the box because the litter is saturated
- Senior cat with PU/PD and weight loss
- Diabetic cat whose insulin dose suddenly seems inadequate
Go to the ER immediately if:
- PU/PD with vomiting, lethargy, and dehydration
- Diabetic cat with breath that smells like fruit or nail polish (DKA)
- Sudden inability to urinate combined with abdominal pain
- Severe lethargy, weakness, or collapse
- Known kidney cat that suddenly stops eating
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Frequently Asked Questions
How much water should a cat normally drink?
A healthy 10-pound cat drinks 7 to 9 ounces (about 200 to 270 mL) of water daily, including water from food. Cats eating canned food drink less from the bowl because their food is 70 to 80 percent water. Cats eating dry food may drink twice as much from the bowl. Doubling of usual intake over several days is the cutoff for veterinary evaluation.
How much does diagnosing PU/PD cost?
An exam plus senior bloodwork, urinalysis, and total T4 typically runs $250 to $500. Adding SDMA, urine culture, and abdominal imaging brings the total to $400 to $800. Ongoing treatment costs vary widely: methimazole for hyperthyroid cats is about $20 to $60 per month, insulin for diabetes is $60 to $150 per month, and kidney diets run $50 to $80 per month.
Can a healthy cat just drink more in hot weather?
Yes — modest increases in summer or with exercise are normal. But the daily total rarely exceeds 50 percent above baseline for environmental reasons alone. Sustained increases lasting more than a week, or any increase paired with weight loss, increased appetite, or vomiting, are not normal and warrant testing.
What's the difference between CKD and chronic renal failure?
They refer to the same disease. Chronic kidney disease (CKD) is the current preferred term; chronic renal failure was the older term. Both describe progressive, irreversible loss of kidney function staged 1 through 4 by the IRIS criteria based on creatinine and SDMA. Most cats are diagnosed in stage 2 or 3 with PU/PD as the presenting sign.
Is excessive thirst always a sign of disease?
In adult cats, yes — almost always. Healthy adult cats are not big drinkers and don't seek out water unless prompted by something. The exceptions are recent diet change (kibble after wet food), high-sodium treats, certain medications, and post-exercise or post-hot-day drinking. Sustained increased thirst lasting more than 3 days needs investigation.
Still Not Sure if Your Cat Needs a Vet?
When you're not sure if this is wait-and-see or call-tonight, Voyage AI Vet triages in under 2 minutes. Describe what you're seeing in chat, share photos of the water bowl, the litter box, and any weight or appetite changes, or hop on a live video call if you want a second pair of eyes. Every answer comes with citations to the actual veterinary literature it's pulling from — so you see exactly where the guidance comes from, not just a chatbot's word.