What is the recommended minimum size for a water supply pipe servicing a group of fixture units?

The recommended minimum size for a water supply pipe servicing a group of fixture units is 1/2 inch. This size is generally accepted in plumbing codes and standards to ensure adequate flow and pressure for typical residential or commercial fixtures. A pipe size of 1/2 inch is capable of delivering sufficient water for kitchens, bathrooms, and other fixture connections when considering the typical demand of multiple fixtures being used simultaneously.

While smaller sizes like 3/8 inch may work for very limited applications, they are generally not sufficient for delivering water to multiple fixtures efficiently. Similarly, larger sizes, while they would certainly accommodate the flow requirements, are often not necessary for typical groupings of fixtures. Thus, adopting a 1/2 inch minimum provides a balance between sufficient capacity and practicality for most plumbing installations.