If the surface is corroded or if the blades are damaged, replace the impeller

Water Pump Impeller Disassembly/Assembly
Water Pump Housing DisassemblyRocker Arm Removal
Squeeze the brake lever slowly and hold it with a band.
Remove the front footpeg bracket bolts.
Raise the rear wheel off the ground with the jack (see
Rear Shock Absorber Removal).
Special Tools - Jack: 57001-1238
Jack Attachment: 57001-1608
Remove:
Lower Rear Shock Absorber B ...
Steering Damper Oil Leak Inspection
Visually inspect the steering damper [A] for oil leakage.
If the oil leakage is found on it, replace the steering
damper with a new one (see Steering Damper Removal/
Installation in the Steering chapter).
ZX1000JD/KD [B]
...
Water Temperature Sensor Inspection
Remove the water temperature sensor (see Water Temperature
Sensor Removal/Installation in the Fuel System
(DFI) chapter).
Suspend the sensor [A] in a container of coolant so that
the temperature-sensing projection [C] is submerged.
Suspend an accurate thermometer [B] with temperature
...