Friend, you say that the pump has low pressure, then you must remove the air in the pump with the sewing nut so that the pressure rises again, if it does not then you will have to do corrective maintenance. The preventive maintenance of a water pump consists of the control of the voltage that is present, whether it is a single-phase, two-phase or three-phase pump, the other is the control of amperage per phase; it has to be the same in the phases If the bearing makes noise, the pump must be uncovered, remove the impeller part of the seal and open the motor to change the bearings. If you only throw water then you have to change the seal