Pipe Sizing and Pressure for Adding Sprinklers to a Well System

A 13 GPM, 1.5 HP well pump runs two zones with 12 Rain Bird Maxi-Paw/Mini-Paw heads on 1-inch laterals. The user wants to add more heads or drip irrigation and asks if upsizing to 1.25-inch pipe will maintain pressure.

Key Principle: Total GPM per Zone

Pressure loss is managed by pipe size, but the real limit is the pump's 13 GPM capacity. Calculate the GPM of each existing and proposed head. The sum per zone must stay under 13 GPM. Upsizing the mainline reduces friction loss but doesn't increase the pump's output.

Recommendation

• Add up nozzle GPM for all heads on a zone.
• If total exceeds 13 GPM, add a new valve/zone rather than overloading existing ones.
• 1-inch lateral is adequate for current flow; 1.25-inch mainline helps but won't create more water.

Drip irrigation uses far less water (1–2 GPM) and can often be added to an existing zone if capacity allows.