https://www.sciencedaily.com/releases/2021/08/210811131552.htm

Now they have data to back it up: Screening for SARS-CoV-2 in wastewater, the team showed they can detect even a single infected, asymptomatic person living or working in a large building. Notification to occupants of each building with positive wastewater increased COVID-19 testing rates by as much as 13-fold. Once an occupant tested positive, isolation and contact tracing helped prevent further spread of the virus.

The approach enabled early detection of 85 percent of COVID-19 cases on the campus, researchers reported in the August 10, 2021 issue of mSystems. In other words, wastewater samples tested positive before most individual case diagnoses.