Why not build the water pump so that it would last the life of the engine. Don't tell me it can't be done, if they can build an engine that will run for 300,000 miles then they can build a water pump that will run that long also.
I don't think you could build a water pump that was driven using magnetic coupling for a reasonable amount of money. A water pump running at speed will require around 2 horse power.
The idea of using a vital system, that if it fails will ruin the engine, to power a device that is designed to fail and fail in such a way as to destroy that vital system is ridiculous. It's the manufacturer telling you to bend over and grab your ankles. The really bad part is that he doesn't even kiss you when he gets done.
Jack