Answer:
Patients with dehydration are given salt-water solution or saline water which creates an isotonic environment with blood cells because the isotonic solution restricts the movement of water by creating an equal concentration of solute and water on both sides of the blood membrane and it prevents any change in the cell size.
The patient is not given pure water because it makes the blood cell hypotonic and water will enter the blood cell, and the cell will swell, which can lead to the death of the patient.