Why is my cat suddenly drinking so much more water than usual?

A real, sustained jump in how much your cat drinks is one of the more reliable early warning signs in cats, not something to wait out. High blood sugar in diabetes, along with several other common conditions, pulls extra water into the urine and forces the body to replace it, which shows up as a cat drinking and urinating noticeably more than her normal pattern. It is easy to miss in a multi-cat home since nobody is measuring the bowl day to day. If you have genuinely noticed more refills or a fuller litter box, treat it as a reason to call the vet rather than a hydration win.

When to call a vet: Get a urine and blood glucose check if the increased drinking has lasted more than a few days, since diabetes, kidney disease and hyperthyroidism all present this way.