Sterilisation of water supply in a motorhome

I have recently bought a new Autosleeper Broadway.   To fill the fresh water tank you have to pump the water through a Whale submersible pump from a container..   After use how can the pump be stored and remain sterile?   After use the pump and pipes are full of water, how do you prevent bacteria multiplying in that water?   How is the tank itself sterilised at the end of the season?