Minnesota

Most Americans use electricity, gas or oil to heat and cool their homes. But the small city of Brainerd, Minn., is turning to something a bit less conventional: the sewer.

As it turns out, a sewer — the place where a city's hot showers, dishwashing water and organic matter end up — is a pretty warm place. That heat can generate energy — meaning a city's sewer system can hold tremendous potential for heating and cooling.

It's just that unexpected energy source that Brainerd hopes to exploit.