Hydraulic head is related to the amount of energy present in a hydraulic system. Hydraulic head is composed of three components: elevation head, pressure head, and velocity head. As water loses one component of its hydraulic head, the other components increase. For example: water that falls 10 feet loses 10 feet of elevation head and gains 10 feet of velocity head. The only way a hydraulic system can lose hydraulic head is through head loss due to friction.