Treated solid waste contains gold, silver and other metals as well as rare elements that are used in electronics and alloys.
Researchers are now looking at identifying the metals that are getting flushed and how they could be recovered.
This could decrease the need for mining and reduce the unwanted release of metals into the environment.
"If you can get rid of some of the nuisance metals that currently limit how much of these bio-solids we can use on fields and forests, and at the same time recover valuable metals and other elements, that is a win-win situation," said Kathleen Smith from the US Geological Survey.
There are metals everywhere. They are in your hair care products, detergents, even nanoparticles that are put in socks to prevent bad odour, Smith added.
Whatever their origin, the wastes containing these metals all end up being funnelled through waste-water treatment plants.
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At treatment plants, waste-water goes through a series of physical, biological and chemical processes. The end products are treated water and bio-solids.
Smith and her team are on a mission to find out exactly what is in our waste.
In the treated waste, Smith's group has already started to discover metals like platinum, silver and gold.
They have observed microscopic-sized metal particles in bio-solids using an electron microscope.
The team is scheduled to present their findings at the 249th national meeting and exposition of the American Chemical Society, the world's largest scientific society, in Denver on Tuesday.