Solution:

Sewage is a water-carried waste matter that is discarded away in sewers and drains. 

It is also known as domestic or municipal wastewater. 

Sewage can be harmful due to several reasons are:

• It includes wastes containing organic matter and microbes which are pathogenic and can cause several water- borne diseases.
• Sewage provides a breeding place for disease causing harmful insects and microbes.
• Sewage is a major cause of polluting drinking water. 
• When sewage enters a lake or stream, it destroys or pollutes the water body affecting the organisms present in the water bodies