What is the hydraulic grade line in a water distribution system?

The hydraulic grade line in a water distribution system is a crucial concept that represents the potential energy available to the fluid at any given point in the system. It is defined as the height to which water would rise in a piezometer or open tube connected to the pipeline, reflecting the static pressure head plus the elevation head of the system.

The correct choice indicates that this line slopes downward in the direction of the flow, which makes sense because as water moves through a system, it experiences losses due to friction and other factors, resulting in decreased pressure and elevation energy. Thus, the slope of the hydraulic grade line illustrates these changes in pressure head and showcases how well the water will flow toward its destination.

The other choices do not accurately represent the nature of the hydraulic grade line. For example, marking the water level in storage tanks pertains to the static level of water but does not capture the dynamics of flow within the distribution system. A constant line representing maximum pressure does not account for the variations in pressure due to friction and elevation changes. Lastly, indicating the temperature of water is unrelated to the hydraulic grade line, which specifically addresses pressure and elevation rather than thermal properties.