Onsite Wastewater Treatment Systems (OWTS)

Onsite (or decentralized) wastewater treatment systems are used to treat wastewater from a home or business and return treated wastewater back into the receiving environment.  They are typically referred to as septic systems, because most involve a septic tank for partial treatment.

The most common and traditional septic systems consist of a septic tank that gravity flows to a soil adsorption field for final treatment and dispersal.  The septic tank allows particulate matter to settle to the bottom of the tank so that large solids do not plug the drain field.  An effluent screen placed in the outlet of the septic tank is used to filter suspended solids out of the effluent.  Final treatment and dispersal of the wastewater takes place in the soil adsorption filed.

A non-traditional system performs the same basic actions as the conventional septic systems.  Differences arise when location, space, laws and regulations, soil type, and/or quantity of wastewater being treated become a limiting factor.  A non-traditional system in this case refers to any OWTS that uses pumps or advanced treatment.  These systems use technologies that require greater frequency of operation and maintenance.


An OWTS can be divided 4 main components:

1. Wastewater Source
2. Collection and Storage
3. Pretreatment Components
4. Final Treatment and Dispersal Components

Pretreatment has two main categories:

1. Advanced Pretreatment
2. Disinfection

Related Resources

interactive_tool_icon   Interactive tool: How a septic system works

Operation and Maintenance Checklist: System Description

Operation and Maintenance Checklist: System Evaluation

Operation and Maintenance Checklist: Site Assessment

Understanding and Maintaining your Septic System

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