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How we manage wastewater overflows

Learn what causes wastewater overflows, what we’re doing to stop them, and what you can do to help.

What is a wastewater (sewage) overflow?

A wastewater (sewage) overflow happens when wastewater spills out from gully traps, manholes, overflow points or pump stations.

This overflow is mainly water, but also contains about 1 per cent human waste, food scraps, fats, debris and trade waste.

When untreated wastewater enters the wider environment, it can pollute property, waterways and beaches.

That’s why we all need to do what we can to stop overflows.

Did you know?

In wet weather, the stormwater from the average roof is equivalent to the wastewater flows from more than 40 households.

Photo of a manhole clogged with tree roots.

Dry weather overflows

In dry weather, most overflows are caused by blocked drains. These blockages happen when people put the wrong waste down the sink or toilet or when a tree root blocks a pipe.

Photo of a house eave with a downpipe connected to it.

Wet weather overflows

In wet weather, stormwater from roofs and roads can overwhelm our pipes. That’s why it’s so important to have your downpipes and gully traps correctly installed.

What we’re doing to help

Our network pipes are built to handle five times the normal wastewater flow so they can accommodate flow at busy times and with population growth. In addition, we're working to reduce overflows through a few initiatives.

Separating wastewater and stormwater networks

In most areas of Auckland, the wastewater and stormwater networks are separate. However, in some older parts of central Auckland, the network is combined, and wastewater and stormwater are carried in the same pipes.

There are projects planned or underway to separate the wastewater and stormwater networks. Some are being carried out by us, and some are being carried out by Auckland Council.

Investing in our wastewater networks

We continuously upgrade and expand our wastewater networks to improve the reliability for customers and reduce overflows.

Inspecting and testing drainage

In addition to monitoring the public network, we also inspect and test private drainage across Auckland. We do this to find out where stormwater is entering the wastewater network.

We inspect wastewater pipes, stormwater downpipes and gully traps in a variety of ways, including:

  • Smoke testing

We pump harmless smoke to pinpoint where stormwater is entering our wastewater network or vice versa.

  • Dye testing

We pour a non-toxic dye down a drain to trace where the water ends up.

  • CCTV camera inspections

We insert a camera down the pipe to inspect internal conditions.

If we need to inspect your property, we will notify you by mail and confirm the time.