There are many types of water filters and filtration systems. You want to put together a filtration system that will best suit your needs. If you only take the RV out a few times each season, your needs are going to be much different than someone who lives in their RV full-time.
For a crash course in RV water filtration go to
RV Water Filter Store: Standard Filter Canisters for Whole RV and read through all of the "Information About
:" topics listed on the left side of the page starting with this link. Very educational and you'll never think of your water the same way again.