A cat who suddenly starts drinking a lot more water usually has a medical reason, and the three most common are chronic kidney disease, diabetes mellitus and hyperthyroidism. Increased thirst is often the very first sign an owner notices — weeks or months before anything else looks wrong. Some causes are harmless, like switching from wet food to dry. But a genuine, sustained increase in drinking is a reason to book a vet appointment, not to wait and see.
How much water should a cat drink?
A commonly cited veterinary benchmark is roughly 45 to 60 ml per kilogram of body weight per day, with anything consistently above about 100 ml per kg per day treated as clearly excessive. For a 4 kg (about 9 lb) cat, that is somewhere near 180 to 240 ml a day in total — and crucially, that total includes the water in her food.
This is why the wet-versus-dry question matters so much. Canned food is around 70 to 80% water, so a cat eating wet food may barely visit the bowl and still be perfectly hydrated. A cat on dry food has to drink nearly all of it. Both are normal.
How do I actually measure it?
Fill the bowl with a measured amount in the morning and measure what is left 24 hours later, with no other water sources available — no dripping tap, no toilet lid up, no plant saucers. Do it for three days and average. In a multi-cat house you may need to separate cats for a day to know who is drinking. Bring that number to your vet; it is far more useful than “she seems to be drinking a lot.”
7 reasons cats drink more water
Short version: kidney disease, diabetes, hyperthyroidism, urinary tract infection, liver disease, certain medications, and a simple change in diet or weather. The first three account for the large majority of cases in middle-aged and older cats.
1. Chronic kidney disease
The most common cause in cats over about seven. Damaged kidneys lose the ability to concentrate urine, so the cat produces large volumes of dilute urine and has to drink more to keep up. The classic pattern is increased thirst plus heavier litter clumps, often with gradual weight loss and a coat that starts to look unkempt. Caught early, diet changes and monitoring can add years.
2. Diabetes mellitus
Excess glucose spills into the urine and pulls water with it. The giveaway combination is drinking and urinating far more while eating well or even ravenously, yet still losing weight. Overweight and older male cats are at higher risk. Feline diabetes is treatable and sometimes goes into remission when caught early, so speed matters here.
3. Hyperthyroidism
An overactive thyroid gland speeds up the whole metabolism. Thirst goes up, appetite goes up dramatically, weight goes down, and many cats become restless, vocal at night or unusually irritable. It is very common in cats over ten and is diagnosed with a straightforward blood test.
4. Urinary tract infection or bladder inflammation
Infection and inflammation cause frequent trips to the litter box, straining, and sometimes blood in the urine. It can look like increased drinking because the cat is also urinating more. A male cat straining in the litter box and producing nothing is an emergency — a urinary blockage can be fatal within a day or two. Do not wait until morning.
5. Liver disease
Less common than the top three but a real cause. Look for yellowing of the gums, eyes or the skin inside the ears, appetite loss, vomiting and lethargy alongside the increased thirst.
6. Medications
Steroids and diuretics both increase thirst and urination as an expected effect. If your cat started a new medication in the last few weeks, this is likely your answer — but confirm with the prescribing vet rather than assuming.
7. Diet, heat or activity change
The benign explanations. Switching from wet food to dry, or from one dry food to a saltier one, raises water intake almost immediately. So does hot weather, a warmer house in winter, or a new water fountain that simply makes drinking more fun. These changes appear at the same time as the trigger and then plateau — they do not creep upward week after week.
When to call the vet
Book an appointment if the increase has lasted more than a few days and you have not changed her food, and go the same day if drinking comes with vomiting, weight loss, appetite loss, lethargy, or straining in the litter box.
Go immediately, out of hours if necessary, for a cat who is trying to urinate without producing anything, crying in the litter box, or hiding and refusing to move. Cats hide illness extremely well, so by the time behaviour changes visibly, something has usually been going on for a while.
Expect your vet to run bloodwork and a urine test. That pair distinguishes kidney disease, diabetes and thyroid problems quickly and cheaply, and all three are far more manageable when caught in the first months rather than the second year.
What to bring to the appointment
Your measured daily water intake, a rough note of how litter box output has changed, her weight if you have a recent one, and any photos of the litter box clumps — unglamorous, but genuinely useful. If you track her weight and vaccine history in one place, bring that too; a weight trend line is worth more than a single reading. Our free app, Lohji, is built for exactly this: medical records, vaccine history, weight logs and voice notes in one place, in 16 languages across 54 countries. It is free, and yes, we make it.
Keeping an eye on it at home
If you are away for long stretches, a camera pointed at the water bowl and litter box is a surprisingly effective early-warning system for exactly these changes — we compared the options in best pet cameras of 2026. And while you are auditing what your cat gets into, it is worth checking that nothing on your windowsill is dangerous: lilies cause acute kidney failure in cats, and kidney failure is one of the causes of increased thirst on this very list.
One more practical note. A cat who is unwell often becomes a cat who slips outside looking for a quiet spot, and a sick cat outdoors is a genuine emergency. Ours is a biased opinion because we sell them, but a lightweight ID tag matters most for the indoor cat everyone assumes will never get out. Shiloh’s House makes $38 designer acrylic NFC smart tags — a finder taps with any phone, no app needed on their end, with engraved details on the back as a backup. Made in the USA, no subscription. We compared the whole category honestly in NFC vs GPS vs metal vs silicone tags.
Frequently asked questions
Is my cat drinking a lot of water a sign of kidney failure?
It can be, and chronic kidney disease is the most common cause in older cats. It is not the only one, though — diabetes and hyperthyroidism produce the same sign. Only bloodwork and a urine test can tell them apart.
Why is my cat drinking from the tap instead of her bowl?
Preference, usually. Many cats favour moving water, and some dislike the bowl’s location, depth or material. Preferring the tap is not itself a warning sign — a change in total volume is.
Can stress make a cat drink more?
Stress more often reduces drinking and eating than increases it. A sustained rise in thirst should be investigated medically first, not written off as nerves about a house move.
Should I limit my cat’s water if she is drinking too much?
No, and this is important. Restricting water in a cat with kidney disease or diabetes causes dangerous dehydration very quickly. Always leave fresh water freely available and get the underlying cause diagnosed.
My cat is drinking more but seems completely fine. Do I still call?
Yes. Increased thirst is frequently the earliest visible sign of all three of the common conditions, appearing well before weight loss or lethargy. Catching them at the “she seems fine” stage is exactly the outcome you want.
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Even indoor cats slip out — especially when they are not feeling well. One tap gets her home.
