This animation focuses on water pollution and its origins ( for both freshwater and salt water).
Although natural phenomena not shown here cause water pollution (volcanism, mineral deposits), it is mostly a result of human activities.
Rivers, lakes and oceans are able to rid themselves of contamination by natural cleansing processes, but only if the pollutants don't exceed specific threshold values.
We have to preserve our drinking water supplies and maintain biodiversity in those ecosystems.
Remember that one third of the world's population do not have safe water to drink.