In water distribution design, what does N+1 pump redundancy indicate?

• A. One additional pump beyond the minimum required
• B. Exactly N pumps
• C. No extra pump
• D. Two extra pumps

Answer: (C)

N+1 pump redundancy means you design the system with one spare pump beyond the minimum number needed to meet demand. The number N is the minimum required to satisfy normal operation, and adding one more ensures you can continue pumping if a pump fails or is offline for maintenance. For example, if four pumps are just enough to meet peak flow, the N+1 setup uses five pumps so that, even with one out of service, the remaining four can still supply the required water. Having no extra pump would leave no backup, while two extra pumps would provide more redundancy than typical practice and incur unnecessary cost.