How clean, both visually and pathogen-wise, would the water in a top class later Roman city have been? How vulnerable would this supply have been? Could a dead sheep fall in and poison the city, or could a rather sinister character dump poison into the channel at some point and cause havok?
Follow up questions:
How would the water have reached my home. Do I go to a public fountain? If so, were there ever examples of access to fountains being controlled by various groups to exert power?
If I was rich enough could I have the water run straight to my house?
Very clean indeed. The public fountains in modern Rome, for example run through the same old Roman water systems, largely, and the water is safe to drink. To answer the other questions, Yes. I don't think so. Yes.