What is being done about wet weather overflows from the network?

In the last three to four years, work has focused on addressing the big challenge of wastewater overflows into the harbour during storms.

Wellington Water has been replacing and repairing many valves, pumps, pipework and electrical components to get the sites working as they were originally designed.

In particular, upgrades to Porirua’s wastewater pump stations are having a large impact at low cost.

Is closure of Titahi Bay beach during heavy rain attributed to the present capacity issues of the treatment plan?

Health warning signs are placed at Titahi Bay after wet weather bypass events and the occasional operational issues with the treatment plant on a precautionary basis – the Bay is not closed but the health risk is higher.  The Wastewater Treatment Plant capacity limitations are currently being rectified and by the end of 2020 it is expected that the plant will have an operational capacity which is more than sufficient to fully treat all wastewater which can be delivered to it. 

In parallel, Porirua City Council and Wellington Water will be investigating how to reduce the adverse effects of stormwater on water quality at Titahi Bay and elsewhere in the city.  That will be a long term issue to resolve and our general advice is that it is not safe to swim for 48 hours after heavy rain anywhere in the Wellington urban area.

Is cross contamination of stormwater and wastewater an issue and will it be investigated and resolved as part of this project?

Yes, this is an issue particularly in the wider network and is contributing to many of the overflows.  That is why we are proposing a network-wide improvement plan and looking at developing a programme of inspections and investigations to reduce ‘inflow and infiltration’. We will also continue to enforce rules around the connection of stormwater pipes to wastewater, which is an ongoing issue.

How are you going to reduce discharges into waterways and the harbour?

We’re investigating the development of increased storage and/or conveyance capacity at key points in the wastewater network as well as the capacity of the treatment plant are key components of improving the wastewater system.

This will help reduce overflows of wastewater from the network as well as managing the flow of water to the treatment plant.

The programme will also work to prevent cross-contamination of stormwater and wastewater, which is currently contributing to overflows.

What is the added capacity to the network and treatment plant going to be - is it future proofed?

Future urban and population growth in Porirua and Wellington City is a fundamental driver for focusing improvements on the wastewater network. The treatment plant itself is highly effective, and recent upgrades have ensured it can meet current flows.

However, we are proposing further capacity upgrades as part of replacing the current discharge consents, which expire in October 2020. This will ensure the treatment plant has ample capacity for projected growth out to 2060.

The other critical component is managing flows of wastewater from the network to the plant during major wet weather events. That is why our focus will not only improve capacity of the plant but enable flow control.

Where are things at with the project?

We lodged an application in April 2020 to renew the treatment plant's resource consents which expire in October 2020.

As part of this, we plan further improvements to the plant, building on upgrades over the last seven years that have improved capacity and enhanced the quality of discharge.

The improvements will increase the capacity of the plant from 1,000 litres to 1,500 litres of wastewater per second. Alongside other technical improvements, this will ensure the treatment plant can fully treat all the flows that reach it and will avoid any bypassing.

The next area of focus for us will be the wastewater network that transports wastewater from your home to the treatment plant.


What do I need to do to make sure the wastewater system works?

The wastewater system is designed for pee, poo and toilet paper. That's it.So to help it work as intended and protect the environment: 

  • Don’t flush wet wipes, paper towels, sanitary products which can clog the system and exacerbate overflows
  • Don't tip fat,oil or grease down the sink - they can create 'fatbergs' that block the pipes


It's also important to understand that the wastewater network starts on your property, with your household plumbing, gully trap and lateral pipes. These feed into the public network that starts outside your property.

You are responsible for looking after your 'private' network. To help keep it shipshape:  

  • Check to ensure roof down pipes aren’t connected to gully traps
  • Ensure gully traps are suitably elevated and protected from the over land flow of stormwater on your property
  • Keep trees clear of your private wastewater laterals
  • Consider purchasing water saving technologies when replacing washing machines, dishwashers, toilets, showers and taps
  • Consider composting food waste rather than using or installing a food waste disposal unit.

Find out more about how you can make a difference in looking after wastewater here