The flint, Michigan water crisis was caused because Flint changed its water source. Since Flint was an older town they still had lead pipes, and when they switched their water source bad thing started to happen.
One of the main problems was because Karegnondi Water Authority (KWA) Flint's new water provider didn't treat their water with phosphate ions like the previous source had. The phosphate ions where helping create kind of a protective layer in the lead pipes. So when it was no longer in the water the pipes started to leak lead, since the pipes were made of lead. Another problem was that the water's ph level was really low. If it had maintained a ph level of more of a 10 then that would have also protected the the pipes since lead's ph level is 11, the water wouldn't have eroded the pipes as much. A third problem was that the chlorine levels in the water were too high. that was caused by the the water source being a run off for salty water in the winter. Since Michigan id cold in the winter, people use a lot of salt for the streets, which then runs of into the rivers.
All this trouble could have been prevented if Flint didn't change it's water source or if the new water had been treated with phosphate ions like the source before them had. Also if the rivers and creeks weren't used as run offs especially in the winter. The rivers shouldn't be used a s run offs any way but if Flint took better precautions then maybe there wouldn't have been as much salt in the water. If the water had been taken better care of and a chemist of a hydrologist had tested the water sooner then maybe this crisis could have been avoided.
A watershed shed is an area of land that drains water that separates water flow. Most if not all the water drains into the same area or body of water. It is almost like a funnel that fills with water and drains into other bodies of water. That water is channel water into soil, groundwater, creek, streams, and eventually making its way to the ocean.
The hydrologic system is a fancy word for the water cycle. It all starts in the atmosphere. Then the cloud fill with water and it rains or snow melts whether it's from the ground or in the mountains. Then the water goes through a water shed and collects in creeks then runs into streams, rivers, lakes, and finally into oceans. once the water gets to the oceans it evaporates and goes back into the atmosphere and does it all over again. Those aren't the only parts either... there are underground streams, plant uptake, fog, dew, and steam from volcanoes.