In hydraulics, how is head expressed?

In hydraulics, head is a measure of the energy of water, which is typically expressed in terms of height. Specifically, head represents the height of a column of water that would produce a certain pressure or energy. The correct way to express head is in feet. This is reflected in option C, which describes head in terms of force (foot-pounds) versus weight (pound) given over height. This unit provides a direct understanding of the potential energy available in a water system, as it relates the energy to the weight of the water.

The other options do not correctly represent the concept of head in hydraulics. Expressing pressure in pounds per square inch is about measuring force on a surface area but does not provide the height measurement that head does. Feet per square foot involves area, which doesn't align with the height context required for head. Cubic feet per second is a unit of flow rate and does not relate to head, which is a measure of potential energy or height in a static column of water.