There are many ways to try and mitigate the problem of EDM currents from VFD controls. Electronic filters, shaft grounding brushes, and insulated ball bearings can help reduce the electrical fluting of ball bearings caused by VFD controls. These can be expensive band aids and do not address the root cause of the problem which is the VFD itself.
The best way to completely eliminate the problem it to do away with the VFD altogether. If the motor requires a soft start, then use a soft starter with a bypass contact. If the motor does not require soft start, then use a standard Across The Line starter. Either way this will completely eliminate the shaft or EDM currents from a VFD, that are the actual cause of the problem.
If the flow rate of the pump needs to be variable, then using a Cycle Stop Valve will easily accomplish this task without any of the problems associated with VFD controls. If the pump was chosen well, restricting the flow with a Cycle Stop Valve will reduce the energy consumption of the pump exactly the same as would a VFD. It is also interesting to note that anytime a pump is running at maximum out put, a VFD causes it to use 5% to 10% more energy than if the pump were running Across The Line using a CSV as flow control.
