2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Sewage is wastewater coming out of households, public places, farms and industry. It also includes rainwater which has flown into the sewers.
Untreated sewage contains harmful chemicals which if released directly into the rivers or seas would pollute them harming the ecosystem of the water bodies and making the water unfit for drinking or further use.