Why are rainwater leaders often excluded from the sanitary drainage system?

Rainwater leaders are typically excluded from the sanitary drainage system primarily because excessive rainwater can overwhelm sewage treatment facilities. When large volumes of rainwater enter the system, they can lead to dilution of sewage, making the treatment process inefficient. Furthermore, the increased flow can cause surcharging, leading to potential overflows or backups, which can introduce untreated sewage into the environment.

By separating the rainwater leaders from the sanitary drainage system, municipalities can more effectively manage stormwater, ensuring that sewage treatment facilities are not overloaded and can operate efficiently. This separation facilitates better control of both wastewater and stormwater management, ultimately protecting water quality and public health.

The other options, while they may touch on relevant points about drainage systems, do not address the primary concern of managing excessive volumes of water introduced by rain, which is crucial in maintaining an efficient and effective sewage treatment process.