Not an RV experienced person. However, lots of experience with storing potable water in tanks for human drinking, bathing, cooking, etc. All this on US Submarines.
The potable water stored in those tanks comes from one of two sources.
At sea, it is pure water made on board by distilling plants that are designed to make water as pure as possible for use in reactor plants.
In port, the water comes from the city or municipal water supply - invariably chlorinated.
On a few occasions I have been involved in having to open up and inspect those potable water tanks and without exception the tanks looked and smelled like they had been used to store human waste!
If you put a fluid that contains minute traces of contamination into a holding tank on a repeated basis, those minute traces over a period of time build up inside the tank. Generally, these tank contaminates are not able to exit the tank over time with the comparatively low flow usages
As we used to say, the walls of those tanks would, "Gag a maggot!"
EDIT: I really didn't consider that fact that the Submarine would be using in terms of thousand of gallons per day - 365 days a year. An RV a lot less!!
Does an RV owner get to see the inside of the potable storage tank on an RV?
No Classified information divulged above. lol