Which Water Pumps on the Gen II Prius are the Problematic Ones?

The inverter coolant pump (electric) is the subject of the recall. The mechanical engine coolant pump is also known for external leakage; sometimes only a very minor leakage, but will likely require replacement at some point during a Gen II's lifetime.

 

as Joe said it is the traditional antifreeze water pump that is problematic.
Sometimes leakage easily seen as pink salts by the belts. Also you may be low on coolant.
Mine leaked at around 90000 miles but holding now at 132000 miles on orig pump.

 

I would have to add that as pointed out the ICE water pump will exhibit leakage over time. However there are cases where the inverter pump have also failed.

As mentioned check for coolant spray on passenger side of engine bay as well as low coolant in the radiator. Checking the overflow bottle can mislead you. It is best to check the radiator itself. It should be full to the top of the neck.

Concerning the inverter pump, check for flow in the inverter coolant reservoir when the Prius is in "Ready Mode". You should see coolant moving through the bottle when looking at is from the side. Also the fluid is normally higher in the back (close to windshield) than the front when in ready mode. No movement of fluid would be a good indication of a failed inverter pump.

There is also a pump for the heater, but not much mention about problems there.

Plus there is a pump for the "thermos bottle". Some folks complain about the pump making excessive noise, but failures are not often.

Our Gen II had the ICE water pump changed at 76K. Changed the belt at the same time. Inverter pump changed on last recall (spring 2013)

Are all of them problematic? Not especially in my opinion. However to expect all of the pumps to last the lifetime of the car would border on far fetched imo based on data available today. I would say simply be aware of the parts within the confines of your Prius and pay attention for any sudden changes.