A backwater valve is a device installed on your sewer pipes that allows sewage to flow out to the public sewer and prevents sewage from backing up into your property. To help determine if your home is required to have a backwater valve installed, refer to Chapter 7 of the California Plumbing Code (CPC) or contact the Sanitation Districts or your local city building department.

Do you need a Backwater Valve?

What's next if you need to install a Backwater Valve?

How to maintain a Backwater Valve.

Diagram courtesty of City of Los Angeles


To identify if a backwater valve already exists on your property, look for an access cover along your private sewer as it exits the building. If a backwater valve does not exist, compare the elevation of the lowest drain on your property to the manhole cover for the public sewer upstream of your property's sewer connection. If the drain is lower than the cover, a backwater valve is required. A licensed plumber can help you determine if a backwater valve exists on your property or if you require one for backflow protection.


If a backwater valve is required according to the California Plumbing Code (CPC 710.1), as a property owner, you are responsible for complying with all applicable building codes to avoid significant costs caused by SSOs or incorrect installations. As such, please take note of the following:

  • Backwater valves are sold through plumbing supply warehouses and some home improvement centers.

  • A plumbing permit and inspection may be required by your local city building department for the installation of a backwater valve.

  • An approved backwater valve must comply with the description provided by CPC 710.6 and must be enclosed in a masonry pit fitted with a removable cover to make it accessible for inspection and repair, unless it is continuously exposed.

  • A backwater valve may not be required downstream of pumps with a check valve and gate valve.

  • Pursuant to the CPC 710.1, cleanouts for drains that pass through a backwater valve shall be clearly identified with a permanent label stating "backwater valve downstream."

  • Refer to the California Plumbing Code for complete requirements.


Property owners are responsible for the proper operation and maintenance of their sewer pipes and backwater valves, if required. Inspect the valve at least once per year to ensure proper operation and flush the entire device and surrounding pipe with a hose to remove any accumulated debris. Contact the valve manufacturer or a plumber for any maintenance questions. Don't ever use the backwater valve as a cleanout. Sewer snakes can damage backwater valves.