A watershed is a group of land whose water collects in one body of water. There a many different factors that could affect the water of a watershed. For example, animals, plants, people, farms and cities.
First, water evaporates from the surface of the ocean. Then, this water vapor turns into clouds through condensation. The clouds move over land and precipitate. This rainwater either seeps into the ground and becomes groundwater, which eventually makes it's way to the ocean or it becomes run-off. Then the cycle begins again and keeps repeating.
It started after the city (Flint, Michigan) decided to change the city's water supply from the Detroit Water and Sewage Department to Karegnondi Water Authority. They had to wait for a new pipe to be built before they could get water so in the meantime they got there water from the Flint River. The water turned a nasty brown color because it was rusting. Water doesn't sound like it should rust but the exposed iron in the old pipes caused it to. The water also had very high lead levels, 13,000 parts per billion to be exact, which gave people rashes.