BACTERIA in sewage and urban run-off sometimes find their way into water
supplies. But where do the bacteria come from in the first place?
Researchers at Vanderbilt University were worried about the extremely high
levels of faecal coliform bacteria in streams in Nashville, Tennessee. Assuming
the bacteria came from human waste, they decided to compare four neighbourhoods,
two connected to the city sewer system, and two which relied on home septic
tanks. They expected to find evidence that septic systems had leaked or
overflowed into the local creeks. But to their surprise, they found no
difference between the four neighbourhoods,…
