[s_q_b]

The concentrations of most of the medications (anti-depressants, contraceptives, antibiotics, etc.) are large in relation to drinking water, but small in relation to the ecosystem into which they're discharged.

Any animal that eats them can usually break them down given their low concentration and half-life, using liver enzymes, and since the majority of the chemicals are human-targeted, they often have much affect on local flora or fauna.

We have bigger problems biggest waster water management anyway. When it rains, your town probably dumps raw sewage into the nearest river through a CSO (Combined Sewer Overflow), which is... less than ideal.

The previously mentioned mechanisms are actually considered eco-friendly approaches in comparison.

So yes, it is a very weird world.