Final answer:
Renin is the enzyme released when blood pressure drops and stimulates a cascade of events for hormones that promote water reabsorption.
Step-by-step explanation:
The enzyme released when blood pressure drops and stimulates a cascade of events for hormones that promote water reabsorption is Renin. Renin acts on angiotensin to form angiotensin I, which is then converted to angiotensin II. Angiotensin II then stimulates the release of aldosterone and the antidiuretic hormone (ADH), which promote water reabsorption.