Water output, or flow rate, is a function of horsepower and pressure. A 50 HP intensifier pump running at 60,000 psi will generally have a maximum output of 1 gallon per minute (gpm). A 100 HP pump running at 60,000 psi will typically put out 2 gpm. This information will help you determine the maximum number of cutting heads that you can use with a pump. Different pump manufacturers will produce slightly different volumes. They may also specify a Maximum Output Pressure and an Operating Output Pressure with different associated water outputs. It is important to verify that the water output specified is what you can expect on a regular production basis (i.e. flow rate based off of Operating Output Pressure).