How do you change a water pump on a peugeot 406 HDI?

To change the water pump on a Peugeot 406 HDI, first, ensure the engine is cool and disconnect the battery. Remove the timing belt cover and the timing belt by loosening the tensioner. Then, detach the old water pump from the engine block, clean the mounting surface, and install the new pump with a new gasket. Finally, reassemble the timing belt, reattach the cover, and reconnect the battery before filling the cooling system with coolant.