Possible causes can range from diabetes, Cushing's disease (increased production of steroids in the body), kidney disease, urinary tract infection or many other possible causes. It is recommended to consult with your veterinarian about the signs that you are seeing at home. Most likely they will run a complete blood work panel which allows them to look for signs of anemia, white blood cell count, kidney and liver values and several other important values. They will also take a urine sample to see how well your pet is concentrating the urine, and for any signs of infection. Sometimes the answer can be as simple as warmer weather causing increased drinking. However, increased drinking and increased urination is something that needs to be addressed with your veterinarian as soon as you notice these symptoms.