A water pressure regulator and an in line filter are must haves if you are going to connect to "city" water. Also it is a very good idea to shut off the city water anytime you are not in the RV. If something starts to leak, left unchecked it can literally ruin your rig.
Excessive water pressure (unregulated), has the greatest potential for disastrous damage but foul water, which we have encountered any number of places coast to coast, will be almost as big a PITA to correct once it gets into your tank and plumbing.
Most places we just fill the tank with filtered water and run off of the pump.
:C