To calculate the amount of water needed to raise the pressure in a cylinder from 50 PSI to 150 PSI, the relationship between pressure, height, and density must be considered. The discussion highlights that while the initial assumption is to triple the water volume to achieve a threefold increase in pressure, this approach does not account for the incompressibility of water. It is emphasized that water behaves differently than an ideal gas, necessitating the inclusion of water's compressibility factor in calculations. The density of water at 50 PSI is noted to be just over 1 g/cm3, and the total volume of water in the pipeline is approximately 57500 cubic feet. Accurate calculations require a deeper understanding of fluid dynamics beyond simple volume adjustments.