How do you know if the water pump needs replacing in a vectra hatch v6 2000?

Look inside the radiator while the engine is running if the pump is good you will see the fluid swirling or at least moving around, if the shaft is difficult to move or there is play in the shaft then the bearings are going bad, if there is coolant seeping out of the weep hole, coolant seeping or leaking from the gasket, if when running with the cap on the hoses never stiffen up ( pressurize ), Overheating issues that cannot be tracked down to the radiator or thermostat, coolant flow is not vigorous.