What is the minimum size of a fixture water supply pipe for a wall hydrant?

The minimum size of a fixture water supply pipe for a wall hydrant is 1/2". This size is designated to ensure sufficient water flow and pressure for various applications associated with wall hydrants, which are often used in outdoor settings for tasks like washing vehicles or watering gardens. A 1/2" pipe is generally recognized in plumbing codes as the appropriate diameter to maintain adequate supply and prevent issues such as low pressure or restricted flow.

Larger sizes like 5/8" or 1" can be beneficial in scenarios requiring higher flow rates, but they are not necessary for the basic function of a wall hydrant, making 1/2" the minimum requirement. Smaller sizes, such as 3/8", would not support the kind of flow expected from a wall hydrant, potentially leading to inadequate performance in situations where more water is needed.