Analysing sewage for traces of coronavirus is helping officials spot outbreaks in areas where relatively few people have been tested.
The government-led scheme is detecting fragments of genetic material from the virus, which pass out from people's bodies when they use the toilet.
More than 90 wastewater treatment sites are now being tested across the UK.
The data collected is being shared with NHS Test and Trace and the devolved administrations, who are using it in their decision-making.
At least 70% of the Welsh population is being monitored by the testing of samples from 24 wastewater treatment sites.
Sewage testing in England is only capturing 22% of the population with 44 participating plants - but the Department for Environment, Food and Rural Affairs said it intends to enlarge the programme.
The initiative extends to another 28 sites in Scotland.
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Professor David Graham, who has been analysing sewage at Newcastle University, acknowledged that countries like the Netherlands have already implemented this nationwide, but said the UK has prioritised accuracy over speed.
After being asked when this would be introduced nationally, he told Sky News: "I'm quite a few steps removed from the decision making process, but I know generally speaking that the aspiration is to have something rolled out that's functional before Christmas."
Bangor University's Professor Davey Jones, who leads sewage testing in Wales and parts of North West England, told Sky News: "In a perfect world, you wouldn't need to do wastewater testing if you were doing unbiased sampling of people.
"The issue that we have is that all of the testing that we're doing is for symptomatic people. We aren't really testing for asymptomatic people."
Up to 80% of people with the virus are asymptomatic.
He believes many of them are schoolchildren.
Prof Jones works closely with Public Health Wales, who use the data provided by his team to help them make decisions about local restrictions.
He said there were concerns about whether English tourists were bringing the infection into Wales, but his research did not show a significant issue and was part of the evidence base for leaving the border open.
Bangor University and the University of Newcastle are also monitoring wastewater from their student halls of residence, in some cases detecting outbreaks before confirmed positive tests.
Sewage sampling discovered a spike in COVID-19 cases in Plymouth too, where local authorities were able to warn residents and health professionals.
Dr Andrew Singer, a lead researcher at the UK Centre for Ecology and Hydrology, said the global efforts to test sewage would not only manage the spread of coronavirus, but also prevent future pandemics from getting out of control.
"Globally we are building the capacity to deliver a public health surveillance programme that has never existed," he told Sky News.
Health Secretary Matt Hancock said: "Monitoring and sampling wastewater offers another tool to help us identify outbreaks early on - helping NHS Test and Trace and local authorities target hotspots quickly and effectively."
Traces of coronavirus in sewage water are not infectious, according to the World Health Organization.
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