Answer: The kidneys will adjust the blood volume to conserve water by lowering the urine output.
This is accomplished as a result of the "Hypothalamus" synthesizing and later releasing "Antidiuretic Hormones" (ADH).
Explanation: The hypothalamus helps to monitor the concentration of solutes (Osmolality) of the blood. When the blood osmolality is increased above the normal level, a signal for thirst is sent.
But when a person is dehydrated the hypothalamus releases ADH which sends signal to the kidney to recover water from the urine.