The kidneys, unfortunately, are often the first organs to get sick in older cats. Drinking a lot may indicate a kidney problem, however, this cannot be determined without an examination. It is advised to have the blood and urine of the cat checked. These examinations can detect the start of kidney damage and therefore, treatment can commence early enough. If you wait until the cat is in really bad shape and showing clear symptoms (thin, scruffy fur, bad appetite etc), it is often already too late for treatment.