A study conducted by the National Institutes of Health indicates that
when medicines are flushed down the toilet, they're often not filtered
from the water at treatment plants because most of the treatment
facilities aren't designed to screen for the specific chemicals. Water
can also break down the medicines after they're dumped in a landfill,
and can seep into ground water.
According to the organization West Michigan
Take Back Meds it's important to properly dispose of medicines
so they don't contaminate the water system. A 2002 analysis by the
U.S. Geological Survey showed that out of 139 streams and rivers in 30
states, about 80 percent of waterways tested had measurable
concentrations of prescription and non-prescription drugs, steroids
and reproductive hormones.