What does it mean to have excessive thirst? 8 cups a day?

Thirst. There are many causes for excessive thirst. The obvious is diabetes mellitus but there are other causes: diabetes insipidus, anxiety, medication side effects, stress, dehydration, thyroid disease, high calcium concentration in blood, high aldosterone level, head injury, brain lesion, too much cortisol in the body, too much growth hormone in the body...