All below grade water supplies, one inch and smaller in size, shall be type K copper ______________________________________.

The requirement that all below-grade water supplies, one inch and smaller in size, must be of one continuous piece of pipe emphasizes the importance of structural integrity and leak prevention in plumbing systems. Using a single continuous piece minimizes the risk of failure at joints, which can be points of weakness where leaks often occur.

A continuous piece of pipe also facilitates a more efficient installation process and reduces the number of fittings needed, which can be a source of potential problems if not properly installed or maintained. Moreover, having a single piece means there are less likely chances for contaminants to enter the system, thereby ensuring better water quality.

While factors such as minimum depth and extension above ground are important for specific applications and protection of the plumbing system, they do not address the critical aspect of the piping's structural quality and reliability as defined by the requirement of a continuous piece. This requirement highlights the need for a practical and effective solution in plumbing installations to avoid complications that could arise from multiple joints or connections.