When a nozzle is operating at an elevation higher than the discharge, elevation pressure is exerted back against the pump. This is roughly equivilant to 5 psi per 10 feet of elevation. The reverse of course is also true as the water will gain pressure when going downhill.
pressure lost as water is used uphill from its source. It is also figured at the rate of .433 pounds per square inch for each foot or .3040 kilograms per square centimeter for each meter of elevation gain.
In hydraulics, the pressure loss caused by raising water through hose or pipe to a higher elevation (roughly equal to one psi for every two-foot increase in elevation above the pump) (11.3 kPa per meter).