'Rhinewater Purification Plant', by Hans Haacke, installed at Museum Haus Lange, Krefeld, Germany in 1972.

'By displaying Krefeld Sewage Plant’s murky discharge, officially treated enough to return to the Rhine River, Haacke brought attention to the plant’s role in degrading the river. By pumping the water through an additional filtration system and using the surplus water to water the museum’s garden, he introduced gray-water reclamation. By displaying samples of water released from the Krefeld sewage plant in large glass bottles in the local museum, Haacke's Rhinewater Purification Plant (1972) increased public awareness of the Rhine River's deterioration. For this work, contaminated water was "pumped into a container where it was filtered and purified before entering a large rectangular basin housing goldfish... The presence of a large fish bowl and the picture-window view into the wooded landscape served as a point of contrast between a life-supporting ecosystem and one on the verge of collapse." Any surplus water was discharged into the garden behind the museum.

From http://www.greenmuseum.org/c/ecovention/sect2.html