I've seen all kinds of filtration units on RV's. From the sophisticated built in ones to real simple portables.
The best one I saw was a top of the line filtration/softener unit but simply put together as a portable. Guy next to me pulled in and brought out a relatively small unit and put it in line within two pieces of hose. Set up time 2 minutes! I asked him about it and was really amazed all the functions that set up provided him for water filtration/softener for the RV.
So it doesn't necessarily have to be an expensive built in one. Lots of options out there.