A watershed is a location of land that has a familiar set of rivers and streams that seeps into a single massive body of water.
In 2014, a large portion of lead made it into water that people in Flint Michigan used for hydration, cleaning, etc; It caused illnesses which developed rashes on your skin and affected kid's education. It was caused when the pipes from the rivers and oceans were changed.
The hydrologic cycle begins with water evaporation from lakes or rivers, then continues with the water forming into clouds, then moisture from the air is transported across the world until it comes across the surface of precipitation. The water will penetrate the land and turn into ground water.