Accessory Dwelling Unit (ADU) Connections for Water, Sanitary and Storm Sewer

Learn more about the requirements that apply to accessory dwelling units related to water, sanitary and stormwater sewer connections.
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Applicants may choose to use a shared meter for the primary structure and the ADU, or have a separate water meter installed for the ADU. Portland Water staff will review each application on a case-by-case basis to see if a single service can be used. They will also determine if an existing service will need to be up-sized. This determination will depend on the total number of plumbing fixtures being served.

Water Supply 

If a single water supply line has been approved through Water the primary dwelling unit and the ADU may use an approved common water supply, provided one of the following criteria is met for each dwelling:

  1. Conversions or additions. Each individual fixture has a shut-off valve or a whole dwelling shut off valve is installed, accessible to both units.
  2. New construction. Each unit is supplied with a control valve accessible to that unit.
  3. The water supply line downstream from the meter may also need to be up-sized depending on the number of fixtures being added.

Shared meter for primary structure and ADU 

When using a shared meter, the meter size will be determined by the total fixture unit count for the entire property. Water will first determine the size of meter the primary structure requires. If, after adding in the additional fixtures for the ADU, the meter requires a larger size, the SDC fees to increase the meter size will be waived if the project qualifies for the ADU SDC Waiver. When increasing the size of an existing meter, fees to change the meter will still apply.
When increasing meter size, it may be necessary to install a new tap in the street to accommodate the larger meter. If a new installation is required, the applicant is responsible for all fees to install the new service line.

Dedicated meter for the ADU

If a dedicated meter is used for the ADU, only fixtures within the ADU will be used to determine the meter size. The maximum SDC credit will be waived. The applicant will be responsible for the service installation fee.

Sanitary and stormwater sewers  

Applicants have the option of connecting the ADU to the existing sanitary sewer system connection or having a separate connection for the ADU. The ADU and the primary dwelling may use a common building sewer line provided:

  • No more than three water closets (toilets) are on a single 3-inch line; and
  • New Fixtures. When the floor level of the ADU is lower than the next uphill manhole cover in the street, a backwater valve(s) for the drain piping serving each new plumbing fixture in the ADU is required. For basement conversions, the drain piping serving the plumbing fixture(s) located above the basement level cannot drain through the backwater valve(s) serving the new basement plumbing fixture(s), and it must connect to the building sewer downstream from the new basement fixture(s). When a backwater valve(s) is installed, it must remain accessible for maintenance and replacement within the ADU.
  • Applicants are required to verify that the existing sewer configurations meets City of Portland standards and meets Bureau of Environmental Services requirements for approved route of service and does not involve "party sewers" or nonconforming connections. Contact BES Nonconforming Sewers Hotline if you have questions (503-823-7189).

If the existing sanitary sewer system connection is used it may be necessary to increase the size of the sewer or wastewater line. In these cases, additional fees will be required.

If a separate connection is made, there will be additional permit and connection fees.

If a new sanitary sewer connection to the public sewer is required, a contractor licensed and bonded for working in the public right-of-way must apply for an Environmental Services sewer lateral permit and establish a “sewer tap.”  Contact the BES Sewer Lateral Connections Hotline if you have questions (503-823-1026).


In most cases, stormwater from either attached or detached ADUs will be required to be disposed of on site. In most cases, installation of a stormwater treatment facility will be required when the ADU creates 500 or more square feet of impervious surface. Refer to the Stormwater Management Manual for specific requirements.

Decommissioning a septic tank or cesspool

If a septic tank or cesspool exists on-site, it must be located. If it is within 10 feet of a new structure, it must be decommissioned. If you are building an addition, and the house was not connected to the sewer when it was built, you will likely need to decommission the cesspool or septic tank.