@NCCindy: recent studies here in MY city especially - showed traces of some of the most frequently prescribed meds, including painkillers like Oxycontin, anti depressants, birth control pills, diabetic meds like Metformin, blood pressure meds, and others - so this isn't just something I made up, OK???? There was a similar warning published in both the Dallas Morning News and Fort Worth Star-Telegram after the TCEQ (Texas Commission on Environmental Quality) published their findings - and before you go off because you're a 'scientist', I've got degrees in geology, geophysics with minors in chem and bio - worked the oil industry and environmental work for 40+ years here - so I think I'm just a little better than the average joe off the street.
You ask about how many pills go down the toilet vs how much water a city consumes - how many pills per annum do you think it takes to titrate out eventually a dose level in a water supply that is readable in parts per million, anyhow?? Apparently enough of this 'flush it' occurs that that's just what's happening - these meds don't get filtered or decomposed by the filtering action that removes most other substances - and once in the water, it just concentrates.
Remember Lake Erie - if you were around then - industrial pollutants, in just parts per million quantities, were dumped into that body of water over decades and decades - nearly rendering one of the largest bodies of fresh water in the world dead, literally - the mercury toxicity alone measured in fish was 300 times acceptable lifetime consumption levels.
NEVER throw active chemicals back into the water supply - EVER - ALWAYS dispose of such items properly. I'm both surprised and taken aback you'd claim to be a 'scientist' and have issue with my remarks - sort of contradictory here.