They've been doing it for years for heavy metals - tracking down illegally dumped slugs of industrial waste into the wastewater stream. Then they introduced qualitative testing for pharmaceuticals, then quantitative testing of same. Their doing viral testing now too - really ramped it up during the vaxscam. The cost is currently prohibitive, but I envision them testing for specific DNA strands in the future. Why? Because they can - and somewhere there's some data aggregation site that will correlate it for nefarious purposes (cough-cough Palantir)...