What is the term for the situation when storm water and domestic sewage enter the same sewer system?

The term that describes a situation where storm water and domestic sewage share the same sewer system is known as a combined sewer. In this system, both types of wastewater flow through a single pipe system to a treatment facility. This design can make it easier to manage the collection of both stormwater runoff and sewage, potentially reducing the infrastructure costs associated with building separate systems.

However, during heavy rainfall or significant storm events, combined sewers may experience overflow. That occurs when the volume of stormwater exceeds the capacity of the system, leading to the discharge of untreated sewage and stormwater into local water bodies. Understanding the implications of combined sewers is crucial for effective wastewater management and environmental protection.