Which water source should be kept away from the drain field?

Stormwater or surface runoff should be kept away from the drain field because it can introduce excessive water to the septic system, overwhelming its capacity to treat wastewater. The drain field relies on a delicate balance of soil absorption and microbial activity to effectively break down contaminants in the effluent. When stormwater or surface runoff infiltrates the drain field, it can dilute the wastewater and reduce the concentration of effluent that reaches the soil, which can hinder the natural treatment process.

Additionally, surface runoff may carry pollutants and sediment into the drain field, which can clog the soil's pores, leading to system failure and contamination of nearby water sources. This contrasts with sources like rainwater that can be absorbed without as significant an impact on the system, groundwater which is naturally present below the drain field, and water from washing machines which, although it needs to be handled carefully, is designed to be processed within the septic system.