Quick answer: A cat drinking noticeably more water than usual is a warning sign — the most common causes are diabetes, chronic kidney disease, and hyperthyroidism, all manageable if caught early.
A healthy cat drinks about 3.5-4.5 oz per 10 lbs of body weight per day. Cats on wet food drink much less since food is ~80% water. If your cat is actively seeking water from multiple sources, emptying the bowl daily, or drinking noticeably more than before, that change is worth investigating.
Diabetes mellitus (often with increased urination and weight loss despite good appetite), chronic kidney disease (most common in cats over 10), and hyperthyroidism (overactive thyroid, usually in cats over 8, often with weight loss and increased appetite). All three are diagnosed with blood and urine tests.
Don't wait to see if it resolves. Increased thirst in cats is almost always medically significant. A basic blood panel and urinalysis at the vet can identify the most common causes quickly. Early diagnosis significantly improves outcomes for all three conditions.
Increased water intake is one of the most actionable early warning signs in cats. A vet visit with blood work is the right response — early treatment makes a real difference for all three common causes.