This was once of today's questions from Jill in Hollywood.  Jill's cat is 18 years old, so my biggest concern is kidney failure (seems to be the number 1 reason very old cats deteriorate).  These cats tend to drink more, and consequently urinate more.  Other possibilities could be a bladder infection, diabetes mellitus, or a behavioral problem.  I suggested she have her cat checked out to first rule out the medical problems (kidney disease, urinary tract infection, or diabetes) before dealing with potential behavior issues.  We'll keep you posted!!!