The established KWR ...

The established KWR water-research institute n the Netherlands has tested for various COVID-19 RNA strings in raw municipal wastewater, with which they started before first reported patients occured in the Netherlands, and repeated couple of times. Not to see if the sewage water is contageous but to see if this set-up would be useful to determine per sewage plant how many of the people are infected...also as a predictive measure after the first peak (which we are experiencing now) has wavered off,  in order to be pro-actively monitoring second/third etc. waves. THey did see a correlation, and propose to the state to instate this methodology.

The amount of patients in the hospital are not a good indication of how many people are actually infected (including the ones not showing any symptoms, but do excrete it with their faeces into the sewer), since only the severe cases of patients end up in hospital. Also the fact that by far not all people who are 'suspect' are being tested, let alone who carry the virus but do not know it...

KWR also tested the effluent of a conventional sewage plant located in the most heavily impacted area of the Netherlands (over-severe stress on the staff and IC rooms in the hospitals): no virus remains came out positive.

Here's the link (Dutch however....google translate?) 

https://utilities.nl/rioolwaterscreening-monitort-verspreiding-coronavirus/