We take a couple 2.5 gallon water jugs with water from the spring that serves the S&B, and buy bottled water to drink and cook. The primary reason is that we don't entirely trust campground water systems. I know, in most states they must be tested and operated as public water systems, but I also know that (a) they aren't all properly tested/operated, and (b) even when they are, the water is not sterile, but contains microbes that the locals have resistance to, but we might not. Since we're not interested in wasting ANY of our precious vacation time acquiring that resistance by being sick for a few days, we are careful about that.
We were at a campground a couple years ago where the folks checking us in mentioned as an afterthought that the campground water had tested contaminated with E Coli, and they were required by law to tell us. But, they hastened to add, they were certain it was safe to drink, they just were required to tell us about the test failures. As a guy whose MS is in water/wastewater chemistry, that was all I needed to hear to know that what they were serving up was shower and toilet water, but bottled water was needed for drinking/cooking.
Y'all are right about keeping your rig's water system clean and disinfected from time to time. And if you are comfy drinking whatever the campground serves up, knock yourselves out. I'll pass, though, thank you very much.