Head loss in a water distribution system main primarily depends on which factors?

Head loss in a water distribution system is primarily influenced by the velocity or rate of flow, the diameter of the pipe, and the roughness of the pipe's interior surface. Each of these factors plays a critical role in how fluid dynamics affect pressure changes within the system.

The velocity or rate of flow is crucial because as water moves faster through the pipes, the friction between the water and the pipe walls increases, leading to greater head loss. A larger diameter pipe allows for a smoother flow of water with less friction, which reduces head loss. Conversely, smaller diameter pipes can significantly increase head loss due to their restrictive nature.

Roughness refers to the texture of the pipe's interior surface. A smoother pipe surface minimizes turbulence and friction, thereby reducing head loss. On the other hand, a rough surface increases resistance to flow, resulting in a higher head loss.

While factors like the type of water source, the layout of the distribution system, and the material of the pipe can influence overall system performance, they do not directly determine the head loss in the same way that flow velocity, pipe diameter, and internal roughness do. Thus, the correct answer accurately emphasizes the most critical factors affecting head loss in a water distribution system.