When compared to a 1-million gallon reservoir at the same water elevation, how much pressure in the mains will a 100,000-gallon reservoir develop?

The pressure in water systems is determined by the height of the water column above a given point, not by the volume of water stored in the reservoir. In this case, both the 1-million-gallon reservoir and the 100,000-gallon reservoir are at the same water elevation, which means that the hydrostatic pressure exerted by the water at the same height will be the same for both reservoirs.

Hydrostatic pressure is calculated using the formula (P = \rho g h), where (P) is pressure, (\rho) is the density of the water, (g) is the acceleration due to gravity, and (h) is the height of the water column. Since both reservoirs have the same height of water (elevation), the pressure in the mains supplied by either reservoir will be identical, regardless of their different sizes.

This fundamental principle of fluid statics explains why the pressure developed in the mains by a 100,000-gallon reservoir at the same elevation is the same as that from a 1-million-gallon reservoir. The volume of water does not factor into the pressure calculation under these circumstances, reinforcing that, for static fluids in containers at the same height, the pressure remains consistent