See related story: Testing the Waters: Fish or Foul?
Slideshow: Testing the Waters: Fish or Foul?
Researchers faced with determining the safety of drinking water have a new approach: If you want to know the quality of the water, ask those who live there -- fish. By Louise Knapp.
Electrodes at the bottom of each fish chamber register gill movements and relay the information to a computer for analysis.Courtesy of William van der Schalie, Army toxicologist at the Center for Environmental Health Research

