Sewage: The wastewater generated by homes, industries, factories, hospitals, schools, etc is called sewage.
Sewer: The drainage pipes carrying the sewage water are known as sewers.
Sewerage: Sewerage is the system of drainage that uses underground networks of pipes called sewers for transporting sewage from the place of generation (i.e. homes, factories, etc.) to the place of processing (i.e. wastewater treatment plants).