Bob - thanks, I was hoping someone with work experience like that would speak up. Being a homebrewer has made me very cautious about sanitation. I bleach sanitize our trailer water system when I put it away for the winter and again in spring when I dewinterize. During the year when we are using it more regularly, I use a peroxide based no-rinse homebrew sanitizer pumped thru the lines when we return home, after draining the system. I use that same sanitizer on our 2 -5 gallon plastic water jugs and our water hose as soon as we get home. I also try to make sure that they are completely dry before storing them.
We try to never put water into the trailer without running it thru an RV carbon water filter and all the water we drink we run thru a Pur pitcher first, but I know neither of those can remove all organic impurities.
I've seen those biofilms you speak of in clear plastic tubing I use to transfer brews between carboys when I have not sanitized and dried them well enough - they are tough to get out even with bleach.
Eric (and Mary who is in no way responsible for anything stupid I post)