https://phys.org/news/2019-01-extremophile-microbes-residential-heaters.html

"Extremophiles are a huge part of the biosphere," said Regina Wilpiszeski, a postdoctoral researcher at Oak Ridge National Laboratory and a recent Penn State doctoral recipient. "If we want to understand what life on Earth is doing, we need to understand it across the board."

The researchers analyzed samples from water heaters in all 50 states, as well as Washington D.C. and Puerto Rico, and found evidence of microbes in about half of the homes. They reported their findings online in the journal Extremophiles.