HI, MY CAT IS ABOUT 12 YEARS OLD AND UP TILL NOW HAS BEEN IN GOOD HEALTH. HE IS A HOUSE PET AND DOES NOT GO AROUND OTHER PETS. JUST TWO DAYS AGO I NOTICED HIS INCREASE IN DRINKING WATER AND URINATING. OTHER THAN THAT HE LOOKS FINE AND HE SEEMS TO EAT WELL. WHAT COULD THIS BE?