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Every day we deliver safe drinking water to your home, and to businesses, through our drinking water network. Once that water has been used in your bathroom, kitchen, laundry and outside, it flows out through private plumbing into the public wastewater network. 

Wastewater is made up of 99 percent water and about 1 percent human and other waste, so it’s important that it is kept separate from the drinking water network. The wastewater network carries wastewater to the treatment plants, where it is treated to remove contaminants before being discharged out to sea.

We work closely with our iwi partners to ensure that wastewater discharges, whether overflows or otherwise, have minimal impact on the environment and do not adversely affect the cultural values and practices attributed to water ways by mana whenua.

The wastewater network

The wastewater network transports wastewater from inside and outside your house via a gully trap and lateral pipes on your property that connect to service branch lines which join the reticulation mains. These carry the wastewater into the largest pipes, the trunk sewers. These are huge pipes - big enough to walk through.

The gully trap and laterals within your property boundary are your responsibility. If there are any blockages or damage to these pipes it is your responsibility to get them repaired by a plumber.

At certain points along the wastewater network there are maintenance chambers/man-holes. Network operators use these as access points to make quick repairs. There are also pump stations at points in the network where wastewater needs to be pumped up a hill, or into the trunk sewer.

The wastewater network leads to the one of the region's wastewater treatment plants. 

Lateral pipes

The lateral pipe connects to your gully trap and direct toilet connections, taking wastewater out of your property to the public wastewater network. This pipe is your responsibility.  This pipe is buried underground and is hard to see. You will usually only realise there is a problem with your lateral pipe when it either leaks up onto the ground or blocks and comes out of your gully trap.  If this happens, please contact a plumber.


The lateral pipe can become damaged over time from tree roots growing beside or into it, land movement, or if it is accidentally damaged during construction or building works.  Take some time to know where your lateral pipe is and avoid planting trees too close or damaging it with gardening work or retaining walls. 

Gully trap

A gully trap is a plumbing feature that should only receive wastewater from your kitchen, bathroom and laundry. It connects to the wastewater network which carries the wastewater to a treatment plant. The top of the gully trap needs to be above ground level to prevent stormwater getting in and it should be partially covered to stop objects getting into the wastewater network but allow flow out onto the ground (and not inside your house) if your wastewater pipe does gets blocked.


The pipe from the roof should connect to the stormwater system, not the sewer/wastewater system. If the downpipes from your roof connect into the gully trap, then you will need to redirect it into the stormwater system.

Wastewater overflows

Wastewater can overflow from the wastewater network into public or private property, waterways and the sea when there is a blockage somewhere in the network or if there is more water than the pipes can carry, for example after heavy rainfall. 

Although the wastewater network is separate from the stormwater network, stormwater can get into the wastewater network and vice versa when private pipes connected to the network from homes are not set up properly. This is called a cross connection.

Reducing wastewater network overflows

Wellington Water is committed to helping protect our harbours, rivers and streams by reducing overflows of untreated wastewater from the networks across Wellington City, Upper Hutt City, Porirua and Hutt City.  We’re working in two different areas:

  • Reducing wet weather overflows caused by rainfall entering the wastewater network
  • Reducing dry weather overflows, which are mainly caused by blockages in older pipes. We’re trialing smart manholes to tell us when there a blockage before it overflows into the street, private property or river and we are increasing our work to replace aging pipes across the network.  You can help reduce blockages by only putting the three P’s into your toilet. 


Overflows during heavy rainfall

For overflows during heavy rainfall, we have historically managed these on a case-by-case basis.  Community and mana whenua expectations for water quality are increasing and we want to move to an improvement strategy, where we assess priorities for investment across the whole network.

We’re working on a process for formalising this in resource consents – one for each city's wastewater network:

  • Porirua including North Wellington
  • Hutt Valley including Upper Hutt and Wainuiomata
  • Wellington including Karori


The consents would set out a collaborative process with mana whenua to:

  • Set future network standards – that is, the volume of overflows we should aim for, taking into account costs and benefits
  • Recommend priorities for improvement.


We’re also proposing community involvement in the process.

The consents will take decades to implement and may involve significant investment from our Councils and ratepayers.  Unfortunately, there is no quick fixes or cheap and easy solutions.  But we know its important work and we are committed to it.

We’ll provide updates on this work here, as it progresses.



Looking after your wastewater - cross connections

One way to help keep our streams, coast and harbours clean for generations to come is to ensure there are no cross connections or wastewater faults on your property - they don’t comply with the Building Act and can cause pollution. Cross connections can cause stormwater to get into the wastewater network. During heavy rainfall, this increases the volume of water and can overload the network’s capacity, which can result in overflowing gully traps, manholes, pump stations, and engineered overflow points into streams, rivers and the sea. 

It is the homeowner’s responsibility to ensure their drainage pipes connect to the right system and are properly maintained. If you are getting drainage work done for an extension or new development, ensure your drainlayer is 100% confident your pipes are going where they should and there are no cross connections.

To avoid wastewater overflows ensure you are only connecting wastewater plumbing to your gully trap. Any outside stormwater, including from roofs, retaining wall drains, driving strip drains, basement pumps or paved area drains, must be diverted to a soak pit or stormwater pipe to road kerb.

Wastewater connections to stormwater pipes have an even more harmful impact. If there is a faulty connection or leak, untreated wastewater can end up directly in the stormwater system and straight into our streams, rivers and the sea until the fault gets repaired. 

More information

For more information, visit Level is the authority on sustainable building, and they have useful information about the compliance requirements for drainage on properties.

Ragmonsters and Fatbergs

Whenever you flush a toilet, have a shower, or unplug a sink, that water flows through your plumbing and into the public wastewater network. It's important that we all look after the region's wastewater network to avoid blockages that take time and money to fix. The two most common things we see in our wastewater network that cause blockages are cooking oil and wet wipes. 

‘Rag Monsters’ - are made up of wet wipes, tampons, sanitary pads, nappies, cloth, hair and other non-biodegradable material, and they should never be flushed down the toilet.

They can block up wastewater pipes – which could cost you a lot of money in plumber bills to repair if the damage happens within your property boundary. If wet-wipes or other items manage to make it all the way to the wastewater treatment plant, they end up blocking the screens at the plant (which may have to be cleared by hand).

These items have no place in the wastewater system and should never be flushed down the toilet.

Put unflushable items into your rubbish bin, and only flush the 3Ps down the loo - pee, poo and paper (toilet paper that is)!


Is it safe to swim?

It is recommended you do not swim for two days following a heavy rainfall event. This is to not only protect you from wastewater overflows, but also other contaminants from stormwater that wash off the roads.

For the latest on swimming in your area, head to LAWA

Resource Consents - Wet Weather Overflows

We require resource consents to legally operate the wastewater network, but they also enable proactive and integrated planning and management to reduce the occurence of wet weather overflows from the network, as we work towards giving effect to Te Mana o te Wai.

You can view these documents below: 

  1. Hutt Valley and Wainuiomata (Part One and Part Two
  2. Porirua (Part One and Part Two)
  3. Wellington (Part One and Part Two

Wastewater Treatment Process

Learn more about how we treat your wastewater

Wastewater Treatment Plants

Monitoring & Testing

Learn more about catchment sampling