My cat has suddenly started drinking loads of water — is it just the hot weather?

Go in, and ask for a blood and urine test. A genuine increase in thirst in a cat is rarely nothing: the three big causes — kidney disease, diabetes and an overactive thyroid — are all found on exactly those tests, and none of them can be ruled out from the sofa.

That said, you named two real confounders. Heat, and a switch from wet food to dry, both honestly raise drinking — wet food covers a lot of a cat's water needs, and dry food does not. So the first job is measuring what she actually takes in, and you can do it with no equipment at all. Fill a measuring jug, top her bowl up only from that jug for 24 hours, shut off the other water sources (including the tap she cries at, just for the day), then measure what's left in the jug and subtract. Hand your vet that number in millilitres, along with her weight and exactly what she eats. Whether it is above what's expected for her is your vet's call, not a threshold you can apply at home — the same figure means different things in a dry-fed 6 kg cat and a wet-fed 3 kg one.

While you're at it, count the litter clumps: more clumps, and bigger ones, is the other half of the picture. Weigh her weekly on a kitchen scale. And if you can catch a urine sample — non-absorbent litter left down for a few hours usually works — bring it with you.

Don't wait for a routine appointment if she is also vomiting, weak, off her food, or breathing quickly. That is a same-day visit.