The treatment process varies from plant to plant, but the goal is the same—separate the solid waste from the liquid waste. In San Francisco, Mike tours a plant where a series of mechanical rakes called a bar screener work to remove as much debris as possible. Next, the sewage travels to one of dozens of different primary sedimentation tanks—the heavier sludge sinks to the bottom, while the liquid rises to the top. Finally, oxygen and disinfectants are added to purify the water.
The finished product from the San Francisco plant is pumped 4 1/2 miles out into the nearest body of water, namely the Pacific Ocean. The final destination of your wastewater depends on your geographic location, and Mike says approximately 18 million gallons end up in the ocean every day. Because the water is now 95 percent treated, it's not harmful to fish or other animals. In fact, it's almost good enough to drink.
Is tap water just treated sewage?
"Sometimes, not all the time," says Mike. "It really depends from state to state."