If your older cat is suddenly emptying the water bowl, drinking from taps, or leaving bigger clumps in the litter box, take it seriously. In senior cats, increased thirst is most often an early sign of kidney disease, hyperthyroidism, or diabetes. All three are common, all three are treatable or manageable, and all three do better when they’re caught early.
The short answer: book a vet visit within the next week or two. Bring a urine sample if you can. Don’t cut back their water while you wait.
How much water is “too much” for a cat?
Most cats drink surprisingly little. A healthy cat needs roughly 40–60 ml of water per kilogram of body weight per day, and that total includes the water in their food. For a typical 4.5 kg (10 lb) cat that works out to about 200–250 ml a day, or roughly one cup.
Where that water comes from depends on diet. Wet food is about 75–80% water, so a cat on mostly wet food may barely touch the bowl, and that’s normal. A cat on dry food has to drink most of its water. Our guide to how much water a cat should drink per day goes through the numbers in more detail.
Veterinary textbooks generally use more than 100 ml/kg/day as the threshold for true excessive thirst, known as polydipsia. You don’t need to measure precisely to spot it, though. These are the signs owners usually notice first:
- The water bowl needs refilling much more often than it used to
- Your cat starts drinking from taps, showers, glasses, or the toilet
- Litter clumps are bigger, or there are more of them
- Accidents outside the box, often because the cat can’t get there in time
- Your cat sits by the water bowl for long stretches
If you want hard numbers for your vet, fill the bowl with a measured amount each morning and measure what’s left 24 hours later. Do this for a few days, keep other water sources out of reach, and allow for evaporation.
The most common causes in older cats
Chronic kidney disease (CKD)
CKD is the most common reason a senior cat starts drinking more. Damaged kidneys lose their ability to concentrate urine. The cat passes larger volumes of dilute urine, then drinks more to make up the loss. Studies estimate CKD affects at least 1 in 3 cats over 15.
Other signs build slowly: weight loss, a patchy appetite, vomiting, a dull coat, and bad breath in later stages. CKD can’t be reversed, but many cats live comfortably for years with diet changes, hydration support, and blood pressure control. The International Renal Interest Society (IRIS) staging system guides that treatment. For more on the early signs, see our article on kidney disease in cats.
Hyperthyroidism
An overactive thyroid speeds up the whole body. It’s the most common hormonal disease in older cats and is estimated to affect around 10% of cats over 10. The classic picture is a cat who is ravenously hungry, losing weight anyway, restless or more vocal, and drinking and peeing more.
It’s very treatable. Options include daily medication, a prescription iodine-restricted diet, or radioactive iodine therapy, which is often curative. One catch: hyperthyroidism can mask kidney disease. Your vet may keep a close eye on kidney values once the thyroid is under control. Our hyperthyroidism guide covers the treatment trade-offs.
Diabetes mellitus
Diabetic cats lose glucose in their urine, and that glucose pulls water out with it. The result is heavy thirst, a lot of urination, and weight loss despite a good or increased appetite. Overweight, middle-aged and older male cats are at higher risk.
Feline diabetes has one encouraging feature. With early insulin therapy and a low-carbohydrate diet, a meaningful share of cats go into remission and no longer need insulin. Published remission rates vary widely between studies, but the window is best in the first months after diagnosis, which is another reason not to wait.
Other causes worth knowing about
- Urinary tract infection. UTIs are more common in older cats, especially those with CKD or diabetes. They can increase drinking and urination.
- Liver disease. Less common, but it can show up as thirst along with vomiting, poor appetite, or yellowing of the gums or eyes.
- Medications. Steroids (prednisolone) and diuretics (furosemide) both commonly increase thirst. If your cat recently started a new drug, mention it.
- Diet or weather changes. Switching from wet to dry food, or a run of hot weather, will raise drinking. These are normal adjustments, not disease. If neither applies, assume something medical until proven otherwise.
What your vet will check
Expect a physical exam, weight check, and questions about appetite, litter box habits, and any weight change. The core tests are usually:
- Bloodwork: kidney values (creatinine, urea, and often SDMA, which can flag kidney decline earlier), blood glucose, and total T4 for thyroid function
- Urinalysis: urine concentration (specific gravity), glucose, protein, and signs of infection. A culture may follow if infection is suspected
- Blood pressure: high blood pressure often travels with kidney disease and hyperthyroidism, and it can damage the eyes. See our article on high blood pressure in senior cats
Many of these overlap with a routine senior screen. The AAHA/AAFP Feline Life Stage Guidelines (2021) recommend more frequent checkups for senior cats, commonly every six months, and our guide to senior cat wellness exams explains what that visit should include.
A practical tip: ask the clinic for a non-absorbent litter kit (plastic beads or aquarium gravel) so you can collect urine at home. A fresh first-morning sample is the most useful for checking concentration.
What you can do at home in the meantime
- Never restrict water. It’s tempting when the litter box is overflowing, but a cat with kidney disease or diabetes can become dangerously dehydrated very quickly. Thirst is compensation, not the problem.
- Add water stations. Wide, shallow bowls in a few rooms make it easier for a stiff older cat to drink without walking far.
- Make the litter box easy. Add an extra box and choose one with a low entry. Scoop more often so your cat isn’t put off by a soggy box. Our article on senior cat litter box accidents has more ideas.
- Write things down. Note when the change started, any weight change, appetite changes, vomiting, and current medications. This makes the vet visit faster and more useful.
- Don’t change the diet yet. Hold off on switching to a “kidney” or “senior” food until you have a diagnosis. The right diet for CKD is different from the right diet for diabetes.
When to see a vet
Book an appointment within a week or two if your senior cat is drinking noticeably more than usual, even if they seem otherwise well. Increased thirst is often the first sign owners can see, sometimes months before anything else.
Go the same day, or to an emergency clinic, if increased thirst comes with any of these:
- Not eating for more than 24 hours, or repeated vomiting
- Lethargy, weakness, or a wobbly, unsteady walk
- Breath that smells sweet, fruity, or like ammonia
- Straining in the litter box or producing little or no urine. In a male cat this can mean a blocked urethra, which is a life-threatening emergency
- Sudden blindness or dilated pupils, which can signal a high blood pressure crisis
The good news is that the common causes of senior thirst are well understood. Kidney disease, hyperthyroidism, and diabetes are all routinely managed in general practice, and cats often do well for years once they’re diagnosed. The cats who struggle most are usually the ones whose thirst was put down to “just getting old.”
Sources: AAHA/AAFP Feline Life Stage Guidelines (2021); International Renal Interest Society (IRIS) staging and treatment guidelines; ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease (Journal of Feline Medicine and Surgery, 2016); AAHA Diabetes Management Guidelines for Dogs and Cats (2018); AAFP Guidelines for the Management of Feline Hyperthyroidism (2016).