Most people would agree that bacteria usually spell trouble where the quality of drinking water is con cerned. However, recent studies conducted by the U.S. Geological Survey (USGS) under the National Water-Quality Assessment (NAWQA) program have shown that some bacteria can improve the quality of water.
Additional publication details
USGS Numbered Series
Some bacteria are beneficial!
U.S. Geological Survey
Colorado Water Science Center, U.S. Geological Survey