To select pipe size, which information must be known?

• A. The distance from the water source
• B. The water demand downstream from each section of pipe
• C. The number of zones
• D. The soil type

Answer: (B)

Sizing a pipe hinges on how much water must move through each section. The crucial fact is the water demand downstream from every section, because that tells you the required flow rate for that run. Once you know the needed flow, you can select a pipe diameter that keeps the flow velocity and pressure losses within acceptable limits to meet the system’s pressure requirements.

Distance from the water source might influence head pressure but doesn’t by itself determine pipe size—without knowing how much water you must deliver, you can’t size the pipe properly. The number of zones relates to layout and control strategy, not the capacity of a given pipe. Soil type affects how the system is installed and how water interacts with the ground, but it doesn’t set the pipe’s hydraulic capacity. So the essential information for selecting pipe size is the downstream water demand.