What is the purpose of a backwater valve?

The purpose of a backwater valve is to prevent sewage from backing up into buildings. This is particularly important in areas where the municipal sewer system may be prone to flooding or surcharging during heavy rain or storms. When there is a risk of sewage rising in the sewer line, the backwater valve automatically closes to block the reverse flow of wastewater, ensuring that the home's plumbing system does not become contaminated and that the interior remains sanitary. This protective measure is critical for maintaining the health and safety of indoor environments, preventing potential property damage and the high costs associated with cleanup and repairs.

Other options do not accurately describe the function of a backwater valve. For instance, draining excess water involves different systems and mechanisms, while regulating flow to fixtures pertains to valves related to pressure and supply, not preventing backflow. Additionally, filtering pollutants is the role of treatment systems rather than a backwater valve.