Water testing is now so good you could just gather samples from the sewage line of various companies to do some testing.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2516581/

http://news.bbc.co.uk/1/hi/world/europe/4746787.stm

https://motherboard.vice.com/en_us/article/z43kk9/the-plan-t...