When flushing fire hydrants, the pressure in the mains should not drop below what level?

When flushing fire hydrants, it is crucial to maintain a minimum pressure in the water mains to ensure that the system continues to operate effectively and safely. A pressure level of at least 20 psi is typically required to maintain adequate flow and prevent disruption to the distribution system. This minimum threshold ensures that the fire hydrant can function properly, allowing sufficient water to be discharged while also avoiding backflow or siphoning effects that might occur if the pressure drops too low.

Maintaining pressure above this level helps in preserving the integrity of the water supply and ensures that other consumers connected to the system are not adversely affected. If the pressure were to drop below 20 psi during flushing, it could lead to potential risks such as water quality issues or insufficient flow in other parts of the distribution network. Hence, the correct answer reflects the established safety and operational standards for flushing fire hydrants in a water distribution system.