We do it every day.

But how many of us think about what happens after we pull the toilet lever?

Increasingly, people in Chicago and across the world are. They’re questioning the sustainability of a system built on using clean water and a lot of energy to process waste, and reimagining the possibilities for what we flush away.

Call it taking the “waste” out of human waste – a movement that includes transforming sewage sludge into fuel, heating buildings with it, using composting toilets to produce fertilizer. It all adds up to a major point: Change is on the horizon, even if that horizon seems far away.

The United States used about 410 billion gallons of water each day in 2005, according to a U.S. Geological Survey report. More than 30 percent of those gallons flush our toilets, which we do five times a day on average, according to the nonprofit American Water Works Association and its Research Foundation in Denver.

Dick Lanyon, executive director of the Metropolitan Water Reclamation District of Greater Chicago, said it costs $747 per million gallons to treat the water. The district serves 5.25 million people.

Added Reed Dring, operations manager for Stickney Water Reclamation Plant, blowers have to pump almost 500,000 cubic feet of air per minute using 20,000 horsepower. “That takes a lot of energy,” Dring said. “Our monthly electric bill is $1.8 million.”

Though the plant offsets some of its costs by using methane gas generated by sewage sludge to heat its buildings, receiving less water would make the job easier, Dring said. “The less (wastewater) to pump, the less motors I have to run.”

Rose George, author of “The Big Necessity: The Unmentionable World of Human Waste and Why It Matters,” said one of the problems with the current sanitation model, one she and others believe is unsustainable, is thinking of “human waste as waste and not a resource.”