Which factor primarily affects the pressure at the bottom of a riser pipe filled with water?

The pressure at the bottom of a riser pipe filled with water is primarily influenced by the height of the water column above it. This principle is derived from hydrostatics, which states that the pressure exerted by a fluid in a vertical column is directly proportional to the height of that column. In practical terms, as the height of the water column increases, the weight of the water above increases, thereby enhancing the pressure exerted at the bottom of the riser.

While factors like the diameter of the pipe, the temperature of the water, and the type of material used for the riser can influence overall system dynamics, they do not directly change the hydrostatic pressure resulting from the height of the water column. For instance, a larger diameter might reduce resistance and improve flow rate, and temperature can affect water density, but the fundamental relationship that height directly relates to hydrostatic pressure remains the primary determining factor for pressure at the bottom of the riser.