Which of the following is essential for calculating the water supply's capacity?

The calculation of a water supply's capacity relies heavily on understanding both static and residual pressures. Static pressure represents the pressure in the system when there is no flow, indicating the potential pressure available in the water supply. Residual pressure, on the other hand, is measured when water is flowing, and it shows how much pressure remains available for firefighting operations.

To effectively assess the capacity of a water supply for firefighting, firefighters need to understand these pressures as they directly influence the volume of water that can be delivered through hoses at a given moment. High static pressure coupled with a substantial residual pressure indicates a capable water supply system, while low residual pressure in comparison to static pressure can signal limitations during firefighting scenarios.

While the size of fire hoses, the hydrant's location, and the distance to the water source are important considerations for fire operations and logistics, they do not directly provide the necessary data for calculating how much water can be supplied under operational conditions, which is the fundamental purpose of evaluating static and residual pressures.