A submersible pump system includes a submersible pump assembly having one or more stages of impellers and a submersible motor assembly that drives the pump assembly. The submersible pump assembly includes a motor housing, a motor within the motor housing for driving the pump assembly and a control module mounted to the motor housing for operating the motor. The control module is electrically connected to a power line and comprises a controller and a variable frequency drive driven by the controller. The controller operates the variable frequency drive to drive the motor to maintain a constant pressure output condition from the pump assembly.