What is considered the basic element of a cold water supply system in a building?

The basic element of a cold water supply system in a building is the riser run outs. Riser run outs are essential components because they deliver water vertically from the main supply line, allowing it to branch out horizontally to various fixtures throughout the building, such as sinks, showers, and other outlets that utilize cold water. This function is vital as it ensures a consistent and adequate supply of cold water to all necessary areas.

In contrast, downspouts primarily serve to channel rainwater from rooftops to the ground, and subsoil drain lines focus on managing groundwater and preventing flooding in basements rather than supplying water for consumption or use. A water closet, while important for sanitation and plumbing systems, is a fixture that utilizes water rather than being a direct part of the water supply infrastructure. Thus, the riser run outs stand out as the core element in establishing a cold water supply system within a building.