I live 7 miles away from a Flying J now Pilot. They have had all kinds of problems with the water going to the RV islands. From freezing in the winter to pipes leaking the summer, you name it. They have replaced it on several occasions and still haven't gotten it right. I have gotten to know one of the maintenance people and they told me that none of the water that goes to the RV or truck islands is filtered or treated, hence they have determined that it is non-potable. On more that one occasion, I have used the water there to flush my black tanks and the rust in the water was amazing. I would not use any water from any truck stop for my tanks. Instead, I would pull into a campground for 1 night get my water that way if necessary.
The other thing with water is after I de-winterize, I want to make sure that I don't have any leaks before heading out on the road. I prefer to put the heat on in the RV, De-winerizer, fill with water and check for leaks. I have done this, regrettably, when the temperature was in the 20's. Running water, from the house to the unit won't freeze. If the unit is setup for cold weather camping, that is also not a problem. Just make sure that you disconnect the hose from the hose bib on the house to keep it from freezing and bring the hose in the house and drain it so it won't freeze.