About Onsite Wastewater Treatment Systems (OWTS)

Overview: Onsite Wastewater Treatment Systems (OWTS), also known as septic systems, are used to treat wastewater that is contaminated by human use, from a home or business, and then released into the environment. OWTS are underground structures that treat and dispose wastewater, typically from homes and businesses in suburban and rural locations. Instead of the wastewater being transported to a wastewater treatment plant, the wastewater is treated on-site.

Conventional OWTS consist of a septic tank and a drainfield system. Wastewater from a house or business drains into a septic tank that is buried underground. The first step in the treatment process is for the solid material in the septic tank to settle on the bottom of the tank, while oil and grease float to the top. The material from a home or business is known as effluent, liquid waste, or sewage discharge. A compartment in the septic tank stops the solid and greasy waste from leaving the tank and the remaining liquid then moves into a drainfield area or distribution system, which is the second step in the treatment process. When the wastewater moves into the drainfield, it filters through the soil, naturally removing any remaining bacteria and is eventually released into the groundwater.

Regulations: Regulations for wastewater treatment systems are created to protect human health and the environment. The State OWTS Policy, required by Assembly Bill (AB) 885, sets standards for wastewater treatment and monitoring requirements. It also authorizes the State, through the Regional Water Boards to authorize local governments to approve OWTS for domestic wastewater through a Local Area Management Program (LAMP). The Los Angeles County Code defines the guidelines and regulations for efficient systems to appropriately dispose of waste through OWTS. If residents and businesses do not follow regulations for wastewater treatment systems, polluted water could be released into the environment. This water may have higher levels of contaminants in it than regulations allow, which may pollute our natural bodies of water where we recreate, swim, or fish. As a result, it may harm animals and the nearby community.

About Non-Conventional Onsite Wastewater Treatment Systems (NOWTS)

Overview: NOWTS are onsite wastewater treatment systems that use a regular septic tank, as well as one or more additional treatment components to treat the effluent before the remaining liquid moves into a drainfield area or distribution system. The additional treatment components may include systems to reduce the nitrogen concentration of the effluent, provide disinfection, or both. High nitrogen concentrations in bodies of water may harm the overall environment where the wastewater is being released.

When there is an excess of nitrogen in groundwater and that groundwater is used for drinking water it can be especially harmful to human infants and young livestock. This can lead to problems with blood circulation in the body, especially for infants under age 4, whose bodies are not yet developed enough to process elevated nitrogen, which causes a condition known as "blue baby syndrome."

Regulations: The Los Angeles County Code defines the guidelines and regulations for wastewater treatment systems to appropriately dispose of waste. Home and business owners that meet the guidelines set by LA County, may be approved for the installation of a conventional onsite wastewater treatment system. In some areas of the County, the rate at which water is absorbed in the soil exceeds guideline standards and local regulations. In these areas, property owners may apply for approval of a non-conventional wastewater treatment system to ensure the proper treatment of wastewater.

The Onsite Wastewater Treatment Program of the Environmental Health Division reviews proposed Onsite Wastewater Treatment Systems designs, work plans, required covenants, historical records, and performs site and installation inspections prior to issuing final system design approvals. System design approvals may be submitted to your local Building and Safety Department to obtain building permits for proposed projects.

Property owners must submit Conventional or Non-Conventional Onsite Wastewater Treatment System plans to any Onsite Wastewater Treatment Program field office or to the Environmental Health Division Headquarters for review. Once approved, stamped and approved plans are then provided to the applicant.

Responsibilities of the Onsite Wastewater Treatment Program include reviewing and approving plans for Conventional and Non-Conventional Onsite Wastewater Treatment Systems within unincorporated areas of Los Angeles County and designated cities that have signed the County’s LAMP MOU.

Conventional Onsite Wastewater Treatment Systems (OWTS)

Home and business property owners that want to install or replace an onsite wastewater treatment system must submit an Onsite Wastewater Treatment System Review Application and the required documents listed on the application to start the OWTS review process.

For more information, view Requirements and Procedures for Conventional and Nonconventional Onsite Wastewater Treatment System

Property owners with existing Onsite Wastewater Treatment Systems must have a system evaluation completed by a qualified professional. If proposing property improvement, property owners are required to go through the plan review process, this includes submitting an Onsite Wastewater Treatment System Review Application , site plan, floor plan, other required documents, and paying applicable fees. Improvements can include, but are not limited to, detached structures, swimming pools, spas, patios, decks, stairs, retaining walls, room additions, ADU/JADU additions, installation of patios, or any permanent structures.

Note: The changes above may increase the volume of wastewater generated, interfere with the existing dispersal system, or eliminate the only suitable area for a future dispersal field.

A System Evaluation Form for Existing OWTS completed by a licensed contractor (Class-A, C-36, C-42) is required if the following conditions apply:

  • System has been in service for more than 15 years
  • The property is a Fire Rebuild
  • No records of prior approval with the project proposals

Refer to the Guide for System Evaluation Form for Existing OWTS/NOWTS for further instructions.

Non-Conventional Onsite Wastewater Treatment Systems (NOWTS)

Home and business property owners that are required to install a NOWTS must submit the Non-Conventional Onsite Wastewater Treatment System (NOWTS) - Covenant and Agreement for the current NOWTS or Non-Conventional Onsite Wastewater Treatment System (NOWTS) - Future Use - Covenant and Agreement .

OWTS Policy Update for ADU and JADU Additions

To support the urgent need for rebuilding efforts post disaster and to expedite the permitting and approval process for Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs), the Los Angeles County Department of Public Health has made a change to its Onsite Wastewater Treatment Systems (OWTS) policy, effective immediately.

This policy update is designed to streamline approvals while continuing to protect public health and environmental quality.

Key Changes in OWTS Requirements for ADU/JADU Additions:

  • Reclassification of ADUs and JADUs:

    ADUs and JADUs will now be considered additional bedrooms rather than independent dwelling units for OWTS evaluation purposes. This change in classification simplifies the process by aligning these additions with existing bedroom-based criteria.

  • Lot Size Flexibility:

    The 2.5-acre minimum lot size requirement for adding ADUs or JADUs has been eliminated. This change increases property owners' flexibility in rebuilding and adding ADU/JADU.

  • Reuse of Existing OWTS:

    Existing OWTS may continue to be used without an upgrade, if they are determined to be adequately sized to accommodate the additional bedroom(s).
    • A system evaluation is mandatory for OWTS systems over 15 years old to assess their functionality and compliance.

  • Expansion Area Requirement:

    A 100% expansion area must be identified and undergo percolation testing if:
    • No prior testing or designation has been done; or
    • The proposed ADU/JADU is located within the existing expansion area or within required setback distances.

  • When OWTS Capacity Is Inadequate:

    If an existing OWTS is found inadequate to handle the additional wastewater load for the proposed additional bedroom(s):
    • The property owner must pursue either a system upgrade or installation of a new OWTS.

A Non-Conventional OWTS (NOWTS) is required for properties near Impaired Water Bodies (polluted water that is unsafe for drinking), regardless of soil percolation test results.

A listing and delisting 303(d) of new impaired water bodies can be reviewed at: 2024 California Integrated Report, Appendix J

  • A feasibility study and percolation testing must support all new or upgraded systems in accordance with DPH/EH Onsite Wastewater Treatment Program (OWTP) guidelines and Regional Water Board standards.

These provisions are consistent with the policies of the California State Water Resources Control Board and the Los Angeles Regional Water Quality Control Board, and they are intended to support safe, effective, and timely rebuilding efforts for affected communities.

Additional Documents

Los Angeles County Department of Public Health (LACDPH) reviews and approves OWTS under the provisions of the LAMP to residents of unincorporated county areas and contracted cities. Cities must adopt the appropriate sections of the Los Angeles County Health and Safety Code (Title 11) and the Los Angeles County Plumbing Code (Title 28) before entering a Memorandum of Understanding (MOU) with the County to be covered under the LAMP’s provisions and restrictions. For more information regarding the LAMP, please visit our LAMP page. LAMP cities that have an MOU with the County include:

  • Agoura Hills
  • Bradbury
  • Duarte
  • Glendora
  • Hidden Hills
  • La Canada Flintridge
  • La Habra Heights
  • La Verne
  • Lomita
  • Lancaster
  • Palmdale
    • ssss
  • Palos Verdes Estates
  • Rancho Palos Verdes
  • Rolling Hills
  • Rolling Hills Estates
  • Santa Clarita

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Report a Problem

If you have questions or concerns about conventional or non-conventional onsite wastewater treatment systems, contact the Onsite Wastewater Treatment Program at (626) 430-5380. For complaints, contact the Environmental Health Call Center at (888) 700-9995 or File a Complaint Online.

Contact Us

Monday - Friday
8:00am - 5:00pm

Tel: (626) 430-5380
Fax: (626) 813-3016

County of Los Angeles Public Health
Environmental Health
Onsite Wastewater Treatment Program
5050 Commerce Drive
Baldwin Park, CA 91706