How Does a Septic System Work

When it comes to rural living or homes without access to municipal sewer lines, the question: How does a septic system work? becomes particularly relevant.

A septic system is an essential component of any such household, serving as a private, on-site wastewater treatment facility. This introduction aims to shed light on the basic principles and components of a septic system, providing homeowners with the knowledge needed to understand, maintain, and appreciate the intricacies of their septic systems. By exploring the functionality of septic tanks, drainfields, and the biological processes at play, readers will gain insights into the effective management of household wastewater in environments where traditional sewer systems are not an option.

What is Septic System?

A septic system is an underground wastewater treatment structure commonly used in rural areas without centralized sewer systems. It uses a combination of nature and proven technology to treat household wastewater from plumbing fixtures (bathroom, kitchen, laundry). This article delves into the workings of a septic system, its components, and maintenance practices.

But how do septic systems work? Here’s how:

Components of a Septic System

The Septic Tank

The septic tank is the first component of a septic system where the initial treatment of waste occurs. It’s a watertight container usually made of concrete, fiberglass, or polyethylene. Its primary function is to hold the wastewater long enough to allow solids to settle down to the bottom (forming sludge), while oil and grease float to the top (forming scum).

The Drainfield

Also known as the leach field or absorption field, the drainfield is a subsurface wastewater disposal area. After the initial treatment in the septic tank, the partially treated wastewater moves to the drainfield. Here, it percolates through the soil, which provides final treatment by removing harmful bacteria, viruses, and nutrients.

How Septic Systems Work: A Detailed Step-by-Step Process

Understanding the intricate process of how a septic system treats household wastewater is essential for proper maintenance and longevity of the system. Here’s a more detailed look at each step of the process:

1. Collection of Wastewater

Origin: All wastewater from your home, including water from toilets, showers, sinks, and laundry, flows through a single main drainage pipe.
Destination: This wastewater is directed into the septic tank, marking the beginning of the treatment process.

2. Treatment in the Septic Tank

Settling: Once in the septic tank, the wastewater is held, allowing heavy solid materials to settle at the bottom, forming a layer known as sludge. Meanwhile, lighter materials, such as oils and grease, float to the top, creating a layer called scum.
Anaerobic Digestion: The middle layer of partially clarified wastewater contains microorganisms that begin the process of breaking down the organic material in the wastewater. This is an anaerobic process (occurs in the absence of oxygen) and helps reduce the volume of solid waste.

3. Transfer to the Drainfield

Effluent Distribution: The partially treated water (effluent) from the tank flows out through a distribution box to a series of underground perforated pipes laid out in the drainfield.
Soil Filtration: As the effluent trickles out of the pipes, through the gravel, and into the soil, it is further purified. The soil acts as a natural filter, removing harmful bacteria, viruses, and certain nutrients.

4. Final Treatment and Dispersion

Biological Treatment: The soil contains microorganisms that continue to treat the effluent by removing or neutralizing contaminants. This biological layer beneath the drainfield is often referred to as the biomat.
Integration into the Water Cycle: Eventually, the treated water is absorbed by the ground, where it may eventually enter groundwater systems. This natural filtration process ensures that the water re-entering the environment is clean and non-polluting.

5. Sludge and Scum Accumulation

Buildup Over Time: Despite the breakdown of organic material, sludge and scum will accumulate in the tank over time. This is why regular inspections and pumping of the tank are crucial to remove these materials and prevent overflow or damage to the system.

6. System Maintenance and Monitoring

Regular Inspections: Professional inspections can identify if and when the septic tank needs to be pumped, preventing the sludge and scum layers from escaping the tank and clogging the drainfield pipes.
Pumping Requirements: The frequency of pumping depends on the size of the tank, the number of people in the household, the volume of water used, and the amount of solids in the wastewater. Generally, tanks are pumped every 3-5 years.

This detailed breakdown of the septic system’s operation highlights the importance of each component and process within the system. Proper maintenance, including regular inspections and pumping, is essential to ensure the system functions efficiently and has a long service life.

Maintenance and Care for Septic Systems

Regular Inspection and Pumping

The septic tank should be inspected by a professional at least every three years, and pumped as necessary, typically every three to five years. Systems with electrical float switches, pumps, or mechanical components should be inspected more frequently.

Efficient Water Use

All the water a household sends down its pipes winds up in its septic system. The more water a household conserves, the less water enters the septic system, reducing the risk of failure.

Proper Waste Disposal

What goes down the drain can have a major impact on how well a septic system works. Materials that decompose slowly (if at all) can fill the septic tank and reduce its efficiency.

Drainfield Care

Parking or driving on your drainfield can damage the underground piping. Planting trees nearby can also lead to roots growing into your system and causing damage. Keeping the drainfield clear of these potential hazards can prolong the life of your system.


Understanding how a septic system works, and how to maintain it, can greatly extend the life of your system and prevent costly repairs. Regular maintenance, efficient water use, and being mindful of what goes down the drain are key to keeping a septic system functioning properly. By respecting these guidelines, homeowners can ensure their system provides effective wastewater treatment for many years.