Combined sewers are systems designed to carry both stormwater and wastewater in a single pipe. This means that during heavy rain, rainwater and sewage flow together to a treatment facility. While this system can be efficient, it can also lead to overflows during heavy storms, causing untreated sewage to enter local waterways. To manage these overflows, cities often implement combined sewer overflow (CSO) controls, such as storage tanks or treatment facilities. These measures help reduce pollution and protect the environment, ensuring that water quality remains safe for both people and wildlife in areas served by combined sewer systems.