The disorder characterized by excessive thirst and urination is diabetes insipidus or diabetes mellitus, with the latter being more common. In diabetes insipidus, the body's ability to concentrate urine is impaired, leading to large volumes of dilute urine and increased thirst as the body tries to compensate for the loss of fluids. Diabetes mellitus is distinguished by high blood sugar levels due to insulin deficiencies or resistance. Both conditions require proper management to prevent dehydration and other complications related to fluid imbalance and blood glucose levels.