Answer:
Rivers
Step-by-step explanation:
Water shed is also known as drainage basin and it is a body of land that drains into a body of water.
Rivers are the largest in terms of volume of a watershed. Other watershed examples include lakes, streams and underground water.
The river has more algae and mircroorgamisms in them. These help in converting harmful substances in the water into non harmful useable substances. This process helps in the filtration of the water.