Brainerd, Minn., is looking into new energy sources to heat and cool homes and businesses. Partnering with Minnesota-based company Hidden Fuels, the city plans to harness the heat in its sewers, reported National Public Radio.

Many types of man-made geothermal energy systems exist around the world. But using heat trapped in sewers, which can build up from dishwasher waste or hot showers, is less common. The system will use technology similar to geothermal heating and cooling systems, but could potentially be less expensive because sewer water is already in the right temperature range (between 42 and 66 degrees Fahrenheit) and much of the infrastructure is already in place.

The challenges come from the mess. "We're not dealing with clean fluids," Hidden Fuels' Peter Nelson said, reported NPR. "We're dealing with contaminated fluids. And so that's really the challenge ... to be able to operate efficiently in that contaminated environment."

Though the system is not yet in place, at one location Hidden Fuels found enough thermal energy to heat 229 homes, reported The city also plans to have a sewer-heated police station by the end of this year.