The average American uses a staggering 60 gallons of water per day for purposes that include flushing toilets, showering and doing laundry. This figure can easily double if outdoor uses, such as watering lawns and filling swimming pools, are also included. Most of that water eventually will become wastewater that must be treated before it can be discharged into nature, which requires a lot of energy. Now scientists are starting to realize that instead of using energy to treat wastewater, it’s possible to actually gain energy from wastewater. In fact, wastewater can contain more than three times the amount of energy needed to treat it. One simple and mature technique for recovering part of this energy is anaerobic digestion, a natural process in which microorganisms feed on grease and other organic materials in wastewater and produce biogas, just as yeast can eat up barley and spit out beer. Biogas contains roughly 50 percent methane, which can be used as a renewable fuel for boilers, furnaces and heating systems or to turn turbines and generate electricity. More advanced techniques, such as hydrothermal processes, take sewage sludge — the solids removed from wastewater during treatment — and convert it into biobased fuels that can be used to replace gasoline and diesel fuel. Beyond energy, scientists are also developing new ways to remove and reuse precious metals that are often found in wastewater. While these techniques are at a very early stage, they seem to have the potential to make wastewater more valuable.