Wastewater-Surveillance COVID-19 Wastewater Surveillance

COVID-19 Wastewater Surveillance


Overhead view of circular tanks at a wastewater treatment plant

The California Department of Public Health (CDPH) and the California State Water Resources Control Board together are coordinating with several wastewater utilities, local health departments, universities and laboratories in California on wastewater surveillance for SARS-CoV-2, the virus causing COVID-19. Data collected from this network of participants, called the California Surveillance of Wastewater Systems (Cal-SuWers) Network, are submitted to the U.S. Centers for Disease Control and Prevention (CDC) National Wastewater Surveillance System (NWSS).

With our local partners, CDPH is monitoring and quantifying levels of SARS-CoV-2  at the headworks or “influent” of 13 wastewater treatment plants. 

What is Wastewater Surveillance?

Looking for SARS-CoV-2 in wastewater can help public health track
the burden of COVID-19 in certain areas

Wastewater surveillance graphic(click image to enlarge)

COVID-19 Wastewater Surveillance Graphic (PDF)

Monitoring wastewater for the presence of infectious pathogens has a history of use in public health. For instance, wastewater monitoring has been used in the past in the surveillance and monitoring of polio virus. During the COVID-19 pandemic, it has been used for the detection and quantification of SARS-CoV-2 virus shed into wastewater via feces of infected persons. Wastewater surveillance tracks “pooled samples” that reflect the overall disease activity for a community serviced by the wastewater treatment plant (an area known as a “sewershed”), rather than tracking samples from individual people. Notably, while SARS-CoV-2 virus is shed fecally by infected persons, COVID-19 is spread primarily through the respiratory route​​ and there is no evidence to date that exposure to treated or untreated wastewater has led to infection with COVID-19.​​ 

Collecting and analyzing wastewater samples for the overall amount of SARS-CoV-2 viral particles present can help inform public health about the level of viral transmission within a community. Data from wastewater testing are not intended to replace existing COVID-19 surveillance systems, but are meant to complement them. While wastewater surveillance cannot determine the exact number of infected persons in the area being monitored, it can provide the overall trend of virus concentration within that community. This can be useful to public health for several key reasons:

  • Fecal shedding of SARS-CoV-2 virus can occur in infected individuals whether or not symptoms are present. 

  • Approximately 90 percent of California households are served by municipal sewage collection systems.

  • Trends of SARS-CoV-2 measurements can provide information on changes in total COVID-19 infection in the community contributing to that sewershed.

  • Wastewater can provide data for communities where COVID-19 clinical testing is underutilized or experiencing limited access.

For national wastewater surveillance data, visit the CDC COVID Data Tracker.

California Data Dashboard

To see participating sites and data collected from the Cal-SuWers Network, please visit the 
CDPH Wastewater Surveillance Network Dashboard

Data Limitations:

Wastewater surveillance for viral detection is still a developing field. Below are some important considerations to keep in mind.

  • It is not possible to reliably and accurately predict the total number of infected individals in a community based on sewage surveillance alone.

  • Wastewater surveillance will not represent homes on septic-based systems.

  • Community-level wastewater surveillance at a wastewater treatment plant will not represent communities or facilities served by decentralized systems, such as prisons, universities, or hospitals that treat their own waste.

  • Low levels of infection in a community may not be captured by sewage surveillance if the quantity of SARS-CoV-2 falls below the limit of detection for lab analysis.

  • Wastewater is a complex environmental sample and inherent variability in measured concentrations are expected due to environmental variability, day-to-day differences in sewershed and population dynamics and laboratory variability. As such, trends (>3 data points) are more reliable than individual data points; concentration of any individual data point may reflect variability and should be interpreted in appropriate context and with caution.

For more information on wastewater surveillance, visit the CDC National Wastewater Surveillance System webpage.

Information for Local Health Departments


The Cal-SuWers Network includes CDPH’s NWSS, which includes participant wastewater treatment utilities and local health jurisdictions, as well as Cal-SuWers Network partners that collaborate and/or contribute data, including academic institutions conducting wasterwater monitoring in California. Other groups in California not listed below also engage in wastewater monitoring but may not contribute data or collaborate directly with the Cal-SuWers Network. Please contact the CDPH wastewater surveillance team (wws@cdph.ca.gov) if you are interested in participating.

Cal-SuWers Network


  • Local health jurisdictions and wastewater utilities from the following counties are currently participating:

    • Alameda, Contra Costa, Fresno, Imperial, Kern, Lake, Los Angeles, Orange, San Bernardino, San Diego and San Francisco

2.​ Cal-SuWers Network Partners:

  • California State Water Resources Control Board

  • UC Berkeley Covid-WEB (Wastewater Epidemiology for the Bay Area)

    • Including participants from Alameda, Contra Costa, Fresno, Imperial, Kern, Los Angeles, Marin, Napa, San Bernardino, San Francisco and Solano counties

  • SCAN (Sewer Coronavirus Alert Network) - Stanford University, Emory University and University of Michigan

    • Including participants from Sacramento, San Francisco, San Mateo, Santa Clara and Yolo counties

    • SCAN also provides data visualization support and a dashboard for all partners of Healthy Central Valley Together

  • UC Davis / UC Merced: Healthy Central Valley Together

    • Including participants from Merced, Stanislaus and Yolo counties

​​​Originally published: February 3, 2022