Recently I saw a show on one of the cable channels; think it was Discovery or Science, which showed bacteria growing in an old flooded copper mine, in water with a very high concentration of copper. Point of the show was, the organisms had adapted to the high Cu+ levels and were precipitating the metal out of the water. (Naturally I can't find the article/show now).
Another show from years ago dealt with use of water lilies used to treat raw sewage. Sewage waste was pumped into one end of a long. shallow trough and slowly moved through water lilies growing hydroponically (SP?) in the trough. as I recall, the water only needed a basic filtering at the other end to be fit for consumption.