Final answer:
The control system of the Type III hydrant system will start the lead pump at a pressure of around 20 psi.
Step-by-step explanation:
The question refers to the Type III hydrant system, which is a system used in firefighting to provide water supply for fire hydrants. The control system of the Type III hydrant system will start the lead pump at a certain pressure, which is determined by the design specifications of the system. This pressure is typically set at around 20 psi (pounds per square inch) to ensure that enough water is being pumped into the system to extinguish fires effectively.