When you flush a toilet or wash dishes, the wastewater has to go somewhere. In cities, it usually flows into a centralized sewer system. But what about homes that aren't connected to a city sewer? That's where a septic system comes in.

Think of a septic system as a small, private wastewater treatment facility right in your yard. Its job is to take all the wastewater from your home, treat it, and safely release it back into the ground. It's a surprisingly common solution. In the United States, more than one in five households rely on a septic system to manage their wastewater.

A septic system is straightforward, consisting of two key components: a septic tank and a drainfield.

All the wastewater from your home flows into the septic tank first. Inside the tank, something simple but important happens: gravity goes to work. Heavier solid waste, called sludge, sinks to the bottom. Lighter materials like grease and oil, called scum, float to the top. This separation leaves a middle layer of relatively clear liquid called effluent.

This liquid effluent is what flows out of the tank and into the drainfield. The drainfield, sometimes called a leach field, distributes the effluent over a large area. The perforated pipes allow the liquid to slowly seep into the surrounding soil. The soil acts as a natural filter, where helpful bacteria and microbes break down any remaining harmful contaminants before the water eventually rejoins the groundwater.

Ready to check your understanding of these core components?

Together, the septic tank and the drainfield form a complete, passive system for treating your home's wastewater on-site.