Western Wastewater Treatment Plant
The Western Wastewater Treatment Plant is managed by Wellington Water on behalf of Wellington City Council and serves approximately 13,000 people.
The facility operated by Veolia is situated in Karori on Wellington’s south coast near the Long Gully Bush Reserve, and Mākara Peak Mountain Bike Park. The plant's discharge point for treated wastewater is in the coastal marine area of Cook Strait, near the Karori Stream mouth. This discharge point has been in operation since 1934.
The Plant began operating in 1997 and was fully commissioned in September 1998. It was granted current consents in July 2010, and they expire 28 July 2035. At the Western Treatment Plant, sewage travels through a series of screens, tanks, bioreactors, clarifiers and ultraviolet treatments before being discharged as liquid into Cook Strait in the vicinity of the Karori Stream Mouth.
Western Wastewater Treatment Plant Overview
Ultraviolet (UV) System Renewal
In January 2026, the plant's UV treatment facility is being replaced. The current equipment is old and unreliable. During this upgrade, UV treatment will continue with no other anticipated impacts on plant operations.
The UV system function is the final part of the wastewater treatment process, and an important part in putting safe, healthy water back into the environment. It involves the use of lamps to emit ultraviolet light to deactivate and disinfect bacteria, viruses and protozoa.
The works, expected to be completed around April 2026, will improve plant’s treatment performance and overall compliance.
For more information about refurbishments at the plant please visit this dedicated webpage: https://www.wellingtonwater.co.nz/projects/western-wastewater-treatment-plant-refurbishment-projects
Resource consents
The Western Treatment Plant was granted new consents on 28 July 2010. These consents will continue for 25 years (expire 28 July 2035).
In general, the consents allow Wellington City Council to:
- discharge of treated and partially treated effluent through an existing outfall,
- to discharge mixed disinfected, treated and milli-screened wastewater during and/or immediately after heavy rainfall,
- the discharge of contaminants to the air,
- and permission to occupy the coastal marine area with an outfall structure.
Resource consents
WGN060283 [37892] Discharge of Treated WW to Coastal Marine Area (Western WWTP)
WGN060283 [35675] Discharge of Partially Treated WW to Fresh Water (Western WWTP)
WGN020236 [22098] Land Occupation by Outfall Structure (Western WWTP)
WGN060283 [25227] Discharge of Treated WW to Fresh Water (Western WWTP)
WGN060283 [25230] Contaminants Discharge to Air (Western WWTP)
WGN060283 [35255] Discharge of Treated WW to Coastal Marine Area (Western WWTP)
WGN060283 [35674] Discharge of Partially Treated WW to Coastal Marine Area (Western WWTP)
WGN160340 [34178] [34179] Pipeline Maintenance Land Use (Western WWTP)
Resource consent reports
Annual Reports:
Western Wastewater Treatment Plant Annual Resource Consents Report 2025/2026
Western Wastewater Treatment Plant Annual Resource Consents Report 2024/2025
Western Wastewater Treatment Plant Annual Resource Consents Report 2023/2024
Western Wastewater Treatment Plant Annual Resource Consents Report 2020/2021
Western Wastewater Treatment Plant Annual Resource Consents Report 2019/2020
Western Wastewater Treatment Plant Annual Resource Consents Report 2021/2022
Western Wastewater Treatment Plant Annual Resource Consents Report 2022/ 23
Quarterly Reports
Western Wastewater Treatment Plant - January - March 2026 - Quarterly Resource Consents Report
Western Wastewater Treatment Plant - July - September 2025 - Quarterly Resource Consents Report
Western Wastewater Treatment Plant - January - March 2025 - Quarterly Resource Consents Report
Western Wastewater Treatment Plant - October - December 2024 - Quarterly Resource Consents Report
Western Wastewater Treatment Plant - July - September 2024 - Quarterly Resource Consents Report
Compliance reports
Western Wastewater Treatment Plant Compliance Report 2020 - 2021
Western Wastewater Treatment Plant Compliance Report 2022 - 2023
Western Wastewater Treatment Plant Compliance Report 2023 - 2024
Appendices
Western Wastewater Treatment Plant Ambient Microbe Monitoring Report May 2026
Western Wastewater Treatment Plant Ambient Microbe Monitoring Report February 2026
Appendix VI Western Wastewater Treatment Plant Outfall Pipeline Report 2025/2026
Appendix III Western Wastewater Treatment Plant Biofilter Assessment 2025/2026
Appendix II Western Wastewater Treatment Plant Biofilter Assessment 2024/2025
Appendix V Western Wastewater Treatment Plant Outfall Pipe Annual Report 2024/2025
Plant performance
Current Status: Compliant
Period: September 2026
Commentary:
The plant is compliant for effluent quality.
Discharges:
There were no unauthorised discharges in September.
Odour complaints:
There was one odour complaint in September. This is thought to be unrelated to the plant.
Items of significance:
There are currently no items of significance for Western.
Read all the Western wastewater treatment plant monthly performance reports
Community Liaison Group Meetings
Newsletters
Kia ora koutou
Welcome to the Western Wastewater Treatment Plant newsletter for May 2026.
In this newsletter we keep you informed about plant operations and initiatives, and the steps we're taking to responsibly manage our impact on local communities and the environment.
In this issue, we update you on:
- plant performance
- projects at the plant.
Plant performance
In March and April, the Western Wastewater Treatment Plant was compliant with consent conditions for total suspended solids (TSS) and faecal coliforms, but not biochemical oxygen demand (BOD). These consent conditions are based on averages of daily results. The daily effluent quality results are meeting quality limits, and the plant met overall compliance by 23 March.
There were no unplanned shutdowns in March and April, and no odour complaints were received.
There were no unauthorised discharges to the Karori Stream in March. There was one wet-weather discharge in April.
There were no notified works in March and April, and only normal routine maintenance activities were undertaken.
A monthly summary of plant performance is published on our website. See Western Wastewater Treatment Plant.
Project updates
There are two projects in early planning stages.
One is looking at optimising sludge production at the plant. We are working with the Sludge Minimisation Facility team funded by Wellington City Council on this.
The other project is looking to renew electrical, instrumentation, and controls (EIC) to support the ongoing reliability and operation of the plant.
We will update you as these work programmes are planned and delivered.
Thank you for taking the time to read this update.
Blair Johnson
Head of Wastewater Contracts
Keep in touch
You are receiving this email because you have expressed an interest in the plant. Please feel free to share this newsletter with others who may also be interested.
Join our mailing list for plant notifications and this monthly update by emailing customer.notifications@wellingtonwater.co.nz.
If you have any questions relating to this newsletter email community@wellingtonwater.co.nz.
For complaints relating to specific incidents or properties go to customer@wellingtonwater.co.nz.