What does the water pressure in a gravity tank system primarily depend on?

In a gravity tank system, the water pressure is primarily determined by the height of the water column above the outlet point. This relationship arises from the basic principles of hydrostatics, where pressure increases with depth due to the weight of the water above it. In this context, as the elevation of the water tank increases—such as when it is placed on the roof of a building—the pressure at the delivery point in the standpipe system also increases because there is more water above that point exerting force due to gravity.

The other factors listed do not have a direct principle affecting pressure in the same way. For instance, while the volume of water can influence the overall supply available, it does not directly affect the pressure delivered by the system at any given point. Similarly, the temperature of the water does not have a significant effect on pressure, as pressure primarily arises from the height of the water column rather than its thermal conditions. Lastly, the material of the tank relates to its structural integrity and potential for leakage or durability, but it does not influence the water pressure itself within the tank system. Therefore, the height of the building, through its effect on the water column, is the critical factor for determining pressure in a gravity tank system.