I don't have any hard facts or documentation either, but I would be worried about doing that. They say not to store drinking water without adding bleach to it because things start to grow after a while, mainly bacteria.
I don't know if that growth would be dangerous to your health if you weren't drinking it or not, but I do know some bacteria can cause some really nasty skin infections. Since there isn't any documentation that it IS safe, I would personally err on the side of caution.
I wonder if distilled water would be any better, but then again how many people have access to distilled water? I think it's pretty expensive to buy, so that probably wouldn't be a good alternative either. If you had a distiller to use, I might check into that more, but otherwise I would not add plain tap water and expect to keep it long term. Just my two cents.