Your Senior Cat Is Drinking More. Here's Why That Matters.

If there is one thing worth knowing about older cats, it's this: a cat who starts drinking more water has a medical problem until proven otherwise.

It is the earliest, most reliable and most frequently missed warning sign in feline medicine. And it's missed because it's easy to interpret as a good thing — *he's finally drinking properly, that must be healthy.*

It isn't. Cats evolved as desert animals and are built to get most of their water from prey. A cat who is noticeably thirsty is compensating for something.

What causes it

Four conditions account for the large majority.

Chronic kidney disease. The most common. Damaged kidneys can't concentrate urine, so the cat loses excess water in urine and drinks to compensate. By the time thirst is obvious, a substantial proportion of kidney function is typically already lost — which is exactly why catching it early matters. Early intervention with diet and management genuinely extends life.

Hyperthyroidism. An overactive thyroid, very common in cats over ten. Classic picture: drinking more, eating more, and losing weight anyway. Often also restless, vocal, with a poor coat, sometimes vomiting. Highly treatable — with medication, diet, surgery or radioactive iodine — and cats often transform on treatment.

Diabetes mellitus. Drinking more, urinating more, often eating more, losing weight. Overweight, older, neutered male cats are over-represented. Manageable, and in some cats caught early, remission is genuinely possible with prompt treatment and diet change.

Urinary tract infection, or less commonly liver disease, hypercalcaemia, or certain cancers.

Two of these — hyperthyroidism and diabetes — are eminently treatable. The third, kidney disease, is manageable and responds meaningfully to early intervention. All four are diagnosed by a blood test and a urine test.

How to actually measure it

"He seems to be drinking more" is hard to judge, particularly in a multi-cat house or a cat with outdoor access.

Do it properly once, and you'll have a real number.

The method:

1. Pick a 24-hour period.

2. Measure the water into the bowl with a measuring jug. Note the volume.

3. Top up during the day if needed, recording each addition.

4. At the same time next day, measure what's left.

5. Subtract. That's roughly the intake.

Corrections worth making: account for evaporation on a hot day by leaving an identical bowl of water somewhere the cat can't reach and measuring the loss from it. Keep other pets away, and keep the cat indoors for the period if possible.

What the numbers mean:

Normal intake is roughly 40–60ml per kilogram of body weight per day, from all sources including food.

• A 4kg cat on wet food might drink very little from the bowl — perhaps 20–50ml — because tinned food is about 75–80% water.
• The same cat on dry food will drink much more, perhaps 150–200ml, and that's normal.

The threshold that matters: more than about 100ml per kg per day is abnormal in any cat. For a 4kg cat, that's 400ml a day — and that warrants investigation regardless of diet.

More useful than any absolute number is change. A cat whose intake has doubled compared to their own previous baseline needs a vet visit, even if the total is still within a "normal" range.

Other signs to look for alongside it

• Larger, heavier clumps in the litter tray, or a tray that needs changing more often. Often the first thing owners notice.
• Urinating outside the tray, particularly if it's a new behaviour
• Weight loss — measure it, don't judge by eye
• Appetite changes in either direction
• A poor, unkempt, greasy or matted coat. Cats stop grooming when they feel unwell.
• Drinking from unusual places — taps, the shower, plant pots, the toilet
• Vomiting
• Bad breath, sometimes with a distinctive ammonia smell in kidney disease
• Weakness in the hind legs or a plantigrade stance — walking on the hocks — which is associated with diabetes

What the vet will do

• Physical exam, including feeling the kidneys and thyroid, and checking body condition
• Blood test — kidney values including SDMA (which detects kidney disease earlier than creatinine alone), thyroid level, glucose, liver values, electrolytes, calcium
• Urinalysis — essential, and sometimes skipped. Urine specific gravity is central to interpreting kidney values, and dilute urine is often the earliest change of all.
• Blood pressure — high blood pressure is common alongside kidney disease and hyperthyroidism, and can cause sudden blindness if untreated
• Possibly imaging

Ask for the urine test specifically. Blood alone can be misleading without it.

Why early detection changes outcomes

This is the part worth emphasising.

Kidney disease: cats diagnosed at an early stage and managed with a therapeutic renal diet, controlled phosphate, blood pressure management and good hydration live substantially longer than cats diagnosed late. The diet in particular has good evidence behind it.

Hyperthyroidism: untreated, it damages the heart and kidneys over time. Treated early, cats often live many more good years.

Diabetes: early, aggressive management with an appropriate diet gives the best chance of remission. Delay reduces that chance considerably.

In each case, the thing standing between early and late diagnosis is usually whether someone noticed the water bowl emptying faster.

The practical habit

For any cat over about eight:

• Weigh monthly. A kitchen or baby scale works. Weigh yourself holding them and subtract if necessary, though a proper small scale is more accurate. A 5% loss matters.
• Measure water intake properly once every couple of months, and any time you have a suspicion.
• Watch the litter tray. You are handling the evidence daily.
• Blood and urine screening annually from about eight, twice yearly from about twelve.

These take very little time and they catch things while they're still worth catching.

Our community tracker logs weight, water intake and litter tray changes with trends drawn over time, and prompts you when something moves outside its usual range. That's the whole reason the tracking side exists — in cats particularly, the numbers change well before the cat looks ill, and by the time a cat looks ill, you've usually lost the window that mattered most.