What is wastewater? Commonly known as sewage, wastewater is the water that goes down the drain from sinks, bathtubs, floor drains & toilets into city sewage systems. Wastewater includes pollutants such as human waste, food scraps, oil, soap, and chemicals that are conveyed via a sewage pipe to wastewater or sewer collection system located in the ground, typically under roads. Nature has a process of treating pollutants in the water, but the amount generated by city large populations would ove...