Lake Springfield in the city of Springfield, Illinois, is a busy place where people swim and fish. The lake also supplies drinking water for Springfield residents and cooling water to a nearby coal-fired power plant. Beautiful homes surround most of the lake. Over the past 15 years, the bacterium Leptospira, commonly found in agricultural animal waste, has been detected in this lake water, and some people have become sick. The contamination of the lake by Leptospira may best be prevented by: