What determines the size of a service pipe?

• A. The diameter of service area
• B. The quantity of water required, the residual pressure required by customer, and pressure of the main
• C. Distance from main
• D. Material of water main

Answer: (B)

Sizing a service pipe comes down to hydraulics: you must ensure the pipe can deliver the needed flow to the customer while keeping the pressure at the customer above a minimum residual level, given the pressure available from the distribution main. The amount of water the customer requires determines how much volume must move through the pipe, so the diameter must be large enough to carry that peak flow without causing excessive velocity or heat losses. The residual pressure at the customer is the minimum pressure you must maintain for reliable service, so the pipe must not drop the pressure below that level under peak demand. The pressure available from the main sets the starting head; if the main can’t provide sufficient pressure, the service line must be sized to minimize losses and still meet the customer’s pressure needs.

Distance from the main and the material of the main don’t directly determine the service size; distance mainly affects losses along the run, which are accounted for in hydraulic calculations, while material affects friction factors but isn’t the primary sizing driver.