Ever since monitoring systems were operational in our sewerage/water supply systems, viruses, including Polio, and many other nasties have consistently been found. It's one of the positive actions consistently taken by the Water Companies. It's a major contribution to tracking such nasties at local and national levels. Whether they're doing enough to eradicate such things getting into our water supply is another question.
Polio has never fully gone away and there is no known cure. The massively successful vaccine program particularly for very young children started many decades ago has meant that infections in the UK and most of the world have been almost eradicated and treatments, when required, highly effective.
The biggest issue is many parents of later generations are not getting their under 5's vaccinated for "fear of what's going in their kids bodies". As that trend continues then expect to see infections re-appearing with horrific consequences.
Yesterday I saw a young mother on the news compare it to the COVID vaccine. Her kids haven't been vaccinated for COVID and are fine, so why get vaccinated against Polio. Staggering ignorance!