I dont get it re covid 19, page-7

So its telling us Covid stays alive in water? After how many days ??? More questions than answers

So 700,000 properties put their water there and they can fnid traces ???? Yet a saliva test cant ????
https://www.abc.net.au/news/2020-09-05/sa-new-coronavirus-cases-in-wastewater-and-hotel-quarantine/12633414