Brewers tasked with turning sewage into suds

This is clean water that used to be waste water but has been treated? What's the issue.

In medieval times people used to brew with water that actually contained waste in order to sanitise it, the yeast killing the bacterea. Then everyone would drink it, including the children.

There is mention of brewing duck pond water (I believe in Davis) in the documentary "How Beer Saved the World". A fun and informative 45min.

https://vimeo.com/23278902