Cities face a big problem: we literally flush money down the drain! Every time we use warm water in sinks or showers, that heat is wasted in the sewer. At the same time, heating our homes is expensive and bad for the planet. The solution is to use special pipes to "catch" that leftover heat from the sewage and send it back into buildings to keep them warm. The benefit is that your energy bills go down because you are using recycled heat. It is a clean, cheap way to stay cozy without needing extra fuel or new power plants.
