The lowest minimum pressure in distribution systems in many states is typically what value?

• A. 10 psi
• B. 30 psi
• C. 20 psi
• D. 40 psi

Answer: (C)

Maintaining a usable, positive pressure at all points in the distribution system is essential for reliable service and fire protection. Many states set a practical baseline so that even at the farthest points or under peak demand, there is enough pressure to deliver water and keep the system from dropping to zero. The value commonly used as the lowest acceptable pressure is about 20 psi. This level is high enough to overcome friction losses and some elevation differences, and to keep hydrants and small services functioning, while not requiring overly large pipes or pumps. Pressures as low as 10 psi are generally considered insufficient for reliable service, and 30 or 40 psi would be higher than the typical minimum that utilities aim for.