The water which gets contaminated after various works; like washing, bathing, mopping, etc. is called wastewater. International Decade for Action on Water for Life (2005 – 2015): It was declared by the General Assembly of the United Nations. Its main goal was to reduce the number of people who do not have access to safe drinking water; by half. Sewage Treatment: The process of removing impurities from waste water before it can be reused or sent to the water bodies is called sewage treatment or cleaning of water. Sewage: The liquid waste which has water as its largest component; along with various types of impurities; is called sewage.