In the weeks ahead, Olympic rowers, sailors, and swimmers will compete in waters with hazardous levels of bacteria. Doctors say that just three teaspoons of Rio’s polluted water are enough to bring on terrible diseases. But one community in Rio shows the way with a cheap and simple device called a “biodigester.” Anaerobic bacteria in the biodigester eat (human) waste and kill pathogens, getting sewage about 80 percent “clean.” Then, it filters through a series of rock-and-plant pods, where the plant roots sanitize it further. From there, the wastewater—now 99 percent clean—flows into the ocean. Environmentalists complain that Brazilian authorities could have implemented many such low-tech solutions to provide the Olympics with a much cleaner environment.