whether you want them, or not
While some chemicals are required, by the Environmental Protection Agency (EPA), to be filtered out of our drinking water, prescription medications are not.
According to this article: http://www.salon.com/2013/03/14/your_tap_water_is_probably_laced_with_anti_depressants_partner/
trace amounts of antidepressants, and other psychotropic prescription medications are found in most urban water supplies.
The impact of this drug residual, on humans, is not known, but it is also in the waters that our sea creatures are living in.
Here are some ways to prevent prescription medications from entering the water supply: