What is the primary factor affecting water pressure in a distribution system during high usage?

The diameter of the main pipe is the primary factor affecting water pressure in a distribution system during high usage because it directly influences the velocity and volume of water that can flow through the system. A larger diameter allows for more water to move through simultaneously, which helps maintain pressure even when a high volume of water is being drawn for consumption. As demand increases, if the pipe diameter is insufficient, it can lead to friction losses and reduced flow rates, resulting in lower pressure at the taps or fixtures.

While other factors like the altitude of the storage tank, water temperature, and pipe material can also influence pressure and flow, they do not have as direct an impact during periods of high usage as the diameter of the main pipe does. For example, while the altitude of the storage tank affects pressure due to gravitational force, it becomes less significant if the pipe is too narrow to handle the demand. Similarly, water temperature can affect viscosity and density, but this impact is minimal compared to the effects of pipe diameter on flow capacity.