There is little disagreement that the potential effects of water contamination on human health and the environment should not be ignored, even though the exact nature of those effects is not yet fully understood. That permanently incapacitating and even lethal substances (asbestos, for example) have, in ignorance, been introduced into the environment may become apparent only decades after their introduction. A new principle in water quality regulation is emerging in response to awareness of these dangers: An individual or organization can be held accountable for hazards to human health or...