Cats descend from desert animals, and healthy cats are famously modest drinkers – much of their water intake historically came from prey, and today from wet food. That is exactly why a cat who suddenly parks itself at the water bowl deserves attention: increased thirst (vets call it polydipsia) is one of the earliest visible signs of several major feline diseases, and catching it early changes outcomes.
What normal looks like
A rough guide is around 50 ml of water per kilogram of body weight per day – for a typical 4 kg cat, about 200 ml, and noticeably less if she eats wet food, which is roughly 80% water itself. A dry-food cat visibly drinks; a wet-food cat may seem to barely drink at all, and both can be normal. What matters most is not the absolute number but change: a cat who used to ignore the bowl and now visits it constantly, empties it, or starts drinking from taps, glasses and toilets.
Innocent explanations first
Hot weather, a switch from wet to dry food, increased activity, and certain medications (notably steroids) all legitimately raise thirst. If a diet change explains the timing, the drinking should stabilise within days. If nothing obvious changed and the drinking persists more than a week – or comes with weight loss, appetite changes or more urine in the litter box – it is time to investigate.
The three big causes vets look for
Chronic kidney disease
The classic disease of older cats. Failing kidneys lose the ability to concentrate urine, so the cat urinates more and drinks to compensate. Other signs: weight loss, dull coat, occasional vomiting, picky appetite. Kidney disease cannot be cured, but diagnosed early it can be managed for years with diet and medication – which is precisely why the thirst clue matters.
Diabetes
Common in overweight, middle-aged, indoor cats. Excess glucose spills into urine and drags water with it: heavy urination, compensatory thirst, and often a ravenous appetite alongside weight loss. Caught early and paired with weight loss and diet change, feline diabetes can sometimes go into remission – some cats come off insulin entirely.
Hyperthyroidism
An overactive thyroid, very common in cats over ten: weight loss despite eating enthusiastically, restlessness, yowling at night, sometimes vomiting – plus increased thirst. Very treatable with medication, diet or radioiodine therapy.
How to actually measure it (the vet will thank you)
Fill the bowl from a measuring jug each morning, measure what remains the next day, and note the difference for a few days. In multi-cat homes this gets harder – separate the suspect cat with her own bowl overnight if you can. Also glance at the litter box: bigger, heavier urine clumps are the other half of this clue. Arriving at the vet with “she drank 320 ml a day for three days, up from about 150” turns a vague concern into a concrete data point.
What the vet will do
A physical exam plus blood and urine tests distinguish the three big causes and a few rarer ones. None of these tests are exotic, and all three major conditions have established treatment paths. Costs vary – our vet costs guide covers typical ranges – but diagnosis is the affordable part; it is late-stage crisis care that gets expensive, which is one more argument for acting on the early sign rather than waiting.
The bottom line: you know your cat’s habits better than anyone. A cat who has become a drinker is telling you something. Measure for three days, then book the appointment.
