Tucked away on the eastern border of the US city of Las Vegas is a dirty secret.
Whenever a toilet is flushed in the city or in unincorporated Clark County, the water flows through a network of 3,540km of pipes, where it is treated to a drinkable standard through solid waste removal and biological treatment.
More than 416,000 litres a day of the recovered water is sent back to Lake Mead via the Las Vegas Wash, allowing Nevada to use more than its very limited annual share of the Colorado River.
“We’re the Disneyland of poop,” said Bud Cranor, a spokesman for the Clark County Water Reclamation District. “The second happiest place on Earth.”
However, the massive quantities of water the facility receives do not only make for a drought solution. They tell a story about Las Vegas that public health officials are just beginning to discover.
By providing the water to outside labs, scientists can quickly detect spikes in disease pathogens such as Covid-19, mpox or influenza.
How and when water is collected
The county’s water reclamation district provides daily samples to Verily, a national health company, as well as less frequent ones to local researchers at UNLV and the Southern Nevada Water Authority.
A continuous sample of raw sewage is collected throughout the day. The on-site lab does not currently allow for pathogen testing, though that may be something the district explores in the future.
Dr Cassius Lockett, the health district’s deputy district health officer of operations, said there had been multiple practical applications of waste water testing. Most recently, the University of Nevada, Las Vegas (UNLV) scientists tested manhole covers around the university and found high levels of mpox, leading the health district to offer a pop-up vaccine clinic in the area.
Testing the water at the reclamation plant circumvents the need to test hundreds of thousands of people on a consistent basis, which is the only way health officials could have previously accessed such a representative sample. “Waste water helps us determine how much of a virus might be in the community – high, medium or low – and what public health actions we need to take or relax to keep the community safe,” Lockett said.
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Lessons from Covid-19
The Covid-19 pandemic spurred the idea of broader waste water testing, said Daniel Gerrity, a principal research scientist at the Southern Nevada Water Authority.
When Verily began conducting daily testing, Gerrity and other researchers could focus in on specific studies and more localised testing in community sewers.
“Waste water surveillance is really effective, and it’s not something that has been used broadly in public health before,” Gerrity said.
What sorts of diseases can waste water testing identify, and how?
Waste water, or sewage, refers to water from homes and buildings, such as toilets, showers, and sinks. Waste water testing can identify different diseases, such as Covid-19 or mpox, caused by viruses.
People infected with these diseases can shed tiny pieces of the virus in their faeces, which can be found in waste water.
By detecting this, scientists can identify the presence of the disease in the waste water. This allows communities to act quickly to prevent its spread (see graphic).
Unlike other methods of monitoring such diseases, waste water testing does not rely on people visiting a doctor, getting tested, or being aware of their illness.
