Final answer:
The issue with combined sewers is that stormwater and sewage are mixed, leading to overflows during heavy rain, which results in water pollution.
Step-by-step explanation:
A potential issue with combined sewers is b that stormwater and sewage are collected in the same sewers. This type of sewer system can become problematic during heavy rainfall events because the volume of stormwater can exceed the capacity of the sewer system. Consequently, combined sewer overflows (CSOs) may occur, leading to the discharge of untreated sewage directly into natural water bodies. This can create significant environmental concerns, including water pollution and public health risks since the discharged effluent contains pollutants such as pathogenic microorganisms, nutrients, and toxic substances. Modern strategies in sewage management favor separate systems for sewage and stormwater to minimize these issues and protect water quality.