Wet weather overflows

Stormwater is rain. During heavy rain, when water is not absorbed by the ground, it needs to be collected so it doesn’t cause flooding. Stormwater is not treated. It flows from downpipes and other stormwater drains directly into the public stormwater network, which empties into streams and the sea at selected points.

Wastewater (sewage), is the used water that goes down sinks, washing machines, shows, baths and toilets. Most of it is water. The rest includes organic matter such as human waste, food scraps, cooking fats and oils, and debris such as sand grit and plastic.

Wastewater drains into gully traps and private wastewater pipes on your property. These connect to the public wastewater network, which carries your household wastewater to a treatment plant.

Wet-weather overflows are a mixture of stormwater (rainwater runoff from roofs and roads) and wastewater (sewage).

In Auckland,

• Watercare is responsible for wastewater (sewage)

• ​Auckland Council is responsible for stormwater. Visit their website

Our network pipes are built to handle five times the normal wastewater (sewage) flow, so that they can accommodate flow at busy times, and population growth.

In most areas of Auckland, the wastewater and stormwater networks are separate.
In central Auckland, they are managed in different ways:

• separate wastewater and stormwater networks

• a wastewater network only: stormwater is left to soak into the ground

• combined networks: the same pipe carries wastewater and stormwater together. This is generally in older parts of the central city.

Most of the time, the combined system (wastewater and stormwater in the same pipes) effectively moves wastewater from private properties to the Mangere Wastewater Treatment Plant.

 
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During heavy rainfall, outfall pipes carry the excess stormwater and wastewater into waterways and out to sea. This helps to prevent overflows onto private property, and protects public health.

The drawback of this system is that the flows may contain some untreated human and industrial waste, toxic materials or debris. As part of our work to reduce overflows, we are replacing combined systems around Auckland.