Water and 12v electric pump?

ayjvee

Hi, spent first few days away in motorhome last week, and thoroughly enjoyed it!  I did notice that of the few others present, they all had a water container outside out of which was a short hose into the van and what looked like a 12v connection next to
it.  Can anyone tell me how this works please, and how it might affect the water heater/tank?  Many thanks.