Is it possible to sink a new well on the site where your "eventual home" will be built and still be within a manageable distance of your now temporary site to supply the TT? It sounds like you are going to need it in the future anyway. Another option may be if the water table into good water isn't too deep, you could sink your own shallow well with a hand pump at your current site. No power needed. I checked into this before but would not work for me due to the fact I need a deep well (130 plus feet to get into good water). Your situation may be the opposite.
And you are correct about the rusty pipe thing. Even with proper filtration, I think it's the idea of all the contaminants in pond water that turn people off to the idea. If pond and lake water was that bad, I would be glowing in the dark, have two heads and three legs by now having spent all of my life living and camping in MI. I probably have swallowed a lot of "pond scum" in my younger years. I'm still here. As Gary mentions, I would still filter as needed and have the water tested. Just to be safe.