As I understand the issue of antibiotics in water, the problem is mostly limited to wastewater.

The biggest issue is the emergence of resistance strains of bacteria due to constant low grade exposure to multiple antibiotics in the effluent stream up to and including sewage treatment plants.

Here is an article that broadly addresses the problem:

https://www.npr.org/sections/health-shot...s-in-raw-sewage

A bit more extensive discussion is here:

https://phys.org/news/2019-03-antibiotic-resistance-wastewater-treatment.htm

You may recall that several years back, there used to be public service announcements that encouraged people to flush unused medications down the toilet. I suspect that many of the baby boomer generation still do as it is a quick and easy way to get rid of whatever medication it was.

Apparently, most of the problem in freshwater systems stems from lakes, where antibiotics and heavy metals can accumulate over time. Most modern freshwater treatment systems (municipal) are effective at removing such contaminates.