Answer:
Diabetes mellitus is a chronic medical condition related to the body's inability to properly maintain blood glucose levels. This is sometimes referred to as "sugar diabetes". Untreated sugar diabetes will result in excessive urination (polyuria) as the body's kidney try to filter excess glucose out of the blood. To counteract polyuria, the body will often exhibit excessive thirst (polydipsia).
Diabetes insipidus is a chronic medical condition related to the body's inability to maintain urinary control. This disorder that results in the body producing excessive amounts of urine (polyuria) and is often characterized by excessive thirst (polydipsia).
People that have mellitus will not experience polyuria if glucose levels are properly maintained as the kidney will not filter excess blood glucose levels. However, people that have insipidus will have urinary control problems, including polyuria, due to insufficient (or inaccessible) anti-diuretic hormone (ADH) that does not return to the bloodstream to prevent additional urinary demands.