What is a septic system?

A septic system is best described as a method for treating household sewage naturally. This system primarily consists of a septic tank and a drain field. When household wastewater enters the septic tank, solids settle at the bottom, where they decompose through biological processes facilitated by anaerobic bacteria. The partially treated effluent then flows into the drain field, where it is further filtered and treated as it percolates through the soil. This natural treatment process reduces pollutants before the wastewater reaches groundwater or nearby waterways.

The other options do not accurately capture the function and design of a septic system. While an underground sewage storage facility may seem related, it does not convey the active treatment process that occurs within a septic system. Additionally, it does not encompass the essential components, such as the drain field, that are crucial for natural sewage treatment. A large-scale wastewater treatment plant refers to centralized systems designed for treating sewage from multiple households or businesses, which is significantly different from the decentralized, self-contained nature of a septic system. Lastly, a filtration system for rainwater is focused on stormwater management rather than the treatment of household wastewater, which is not the core function of a septic system.