Good to know you added the pressure regulator....my advice...run the water from the park tap for 30 seconds or so in case it's been a while since it was last used. Also, I spray Lysol disinfectant around the spigot. Some people put their sewer hose right up against those to rinse out their hose or touch the spigot with their dirty hands after handling their sewer hose. With regards to your water filter, is it one of the blue ones you add to the tap...if so run water through it a few seconds too, and when you are not using the trailer between trips, stick that filter in the fridge.
2011 GMC Sierra 2500HD
2014 Rockwood 8289WS, Diamond Pkg.