Cats that eat wet food get much of their fluid from their food and may therefore drink quite little. A cat that suddenly starts looking for water more often, or produces larger amounts of urine, has a change that is worth following up. Kidney disease, diabetes and hyperthyroidism are some of the diseases that can cause increased thirst and urination.
Notice whether your cat is losing weight, eating more or less than before, vomiting, becoming restless or, on the contrary, more tired. Changes in the litter tray can also give clues, such as larger clumps of urine. The vet often uses blood and urine tests as a first step and builds on the investigation based on the results.
Book an appointment if the thirst or the amount of urine has clearly increased and the change persists. Do not wait until your cat has become thin or clearly ill, as several of the most common causes can develop gradually.