What is a primary drawback of combined sewers?

The primary drawback of combined sewers is that they can have an increased risk of overflow during rain events. Combined sewers are designed to handle both stormwater and sewage in a single pipe system. During periods of heavy rainfall, the volume of water can exceed the capacity of the sewer system, leading to overflows. This condition, known as combined sewer overflow (CSO), can result in untreated sewage and stormwater being discharged into local water bodies, which poses environmental and public health risks.

In such scenarios, the ability of the system to effectively manage both sewage and rainfall is compromised, leading to potential contamination and ecological harm. Understanding this characteristic of combined sewers emphasizes the importance of proper management and the need for alternatives, especially in urban areas where heavy rainfall is common.

While it is true that combined sewers may also relate to considerations regarding maintenance and cost-effectiveness, those aspects do not directly address the immediate and significant environmental concern posed by overflow during rain events.