All below grade water supplies, one inch and smaller in size, shall be made of what type of copper?

For water supplies that are located below grade and are one inch in diameter or smaller, Type K copper is the appropriate choice due to its thicker walls and higher level of durability and resistance to corrosion compared to other types of copper. This type of copper is recommended for applications where the piping may be exposed to harsher conditions, which can include contact with soil, moisture, and potential physical impacts.

Type K copper's thicker dimensions provide strength and longevity in underground environments, helping to prevent leaks and reduce the risk of failure over time. In contrast, although Types L and M copper pipes are also used in plumbing systems, they are not specified for below grade uses in these scenarios, primarily due to their thinner walls and reduced structural integrity when faced with soil pressure or other environmental factors. Type R copper is not a standard designation commonly referred to within plumbing codes, so it would not apply in this context.