In deep sea, the pressure of the water is tremendously high. Hence the body of the submarine is thick and built by strong material
When measuring blood pressure, the inflatable cuff of the sphygmomanometer should be at the same level with the heart so that the pressure measured is equal to the blood pressure of the heart.
For intravenous transfusion (IV), the bottle is hung at an elevated position to ensure that the liquid in the IV bottle gains sufficient pressure to flow into the vein of the patient.
The water tower is built at high place so that the water has sufficient pressure to flow to consumer’s house.