Too_Many_Tools fired this volley in
:

Anyone who thinks what is flushed down the drain doesn't end up back
into your water supply does not understand science.

TMT, you paint the subject with too broad a brush.

IF you specify a particular chemical, you may say, "This does (or does
not) stay in the water." Not all chemicals do, and household bleach -
which was mentioned - is one of the ones that completely decomposes,
quickly.

Don't fall into believing the nanny-state mantra that ALL things
artificial are automatically permanent pollutants. They aren't.

LLoyd