Baroreflex is a reflex triggered when a baroreceptor is stimulated. In the human body, baroreceptors are found in the carotid sinuses and the sinus of the aorta. These receptors are stimulated during changes in blood pressure. Baroreceptors are sensitive to the stretching of blood vessels.
As blood pressure rises, baroreceptors transmit nerve impulses to the vasomotor center of the medulla oblongata, which is then inhibited. This results in vasodilatation of the blood vessels to reduce blood pressure.
You shouldn't allow yourself to be re-hydrates in this way because it is incredibly unsafe. Tap and bottled water can carry bacteria which can cause severe infections to get into the bloodstream.