Final answer:
Diabetes insipidus is caused by antidiuretic hormone (ADH) hyposecretion, leading to increased urine production and thirst due to the kidneys being unable to retain water.
Step-by-step explanation:
Diabetes insipidus is caused by antidiuretic hormone (ADH) hyposecretion. This condition occurs when the posterior pituitary gland does not secrete sufficient amounts of ADH, resulting in the kidneys not being able to retain water. Consequently, this leads to a significant increase in urine production (polyuria) and thirst (polydipsia), although drinking more water does not decrease blood solute concentration because of the low ADH levels preventing water reabsorption. Severe cases of diabetes insipidus can lead to dehydration and electrolyte imbalances.