Wastewater journey

From toilet to treatment

Flush your toilet or pull the plug on the sink and the wastewater disappears. Out of sight, out of mind. But have you ever thought about where it goes?

The wastewater journey, from your house to its final destination, is far from simple. From the pipes on your property, through our network of underground pipes and onto a wastewater treatment plant - it's not a journey without obstacles.

How wastewater is treated

Every day over 6.5 million litres of wastewater comes into our 11 treatment plants. The way it's treated varies across our plants, but in general it goes through up to four levels of treatment to suit the way it’s being reused or returned to the environment.

Screening

Before the treatment process starts, raw wastewater goes through screens to filter out things that shouldn't have been flushed - wet wipes, rags, debris and other objects. These materials often don't make it this far as they act as obstacles that snag, build up and block pipes earlier in the network.

Removing the non-flushables that make it here, which get taken to landfill, helps to protect pumps and other equipment further downstream.

Separation

After screening, there’s a settling process to remove sand and grit. Then the wastewater moves into tanks where the solids separate from liquid and settle to the bottom.

At the Taupō wastewater treatment plant, those solids spend about 20 days in a digester before going to a farm where worms turn it into vermicast, a sought-after natural fertiliser.

Removing nutrients

The remaining liquid continues on and is treated further in sedimentation tanks and biological filters. The partially-treated water moves into clarifiers where any remaining solids settle out. These solids (known as sludge) are collected and sent for further treatment.

With the sludge removed, the wastewater is pumped onto a series of filters where bacteria strip out the dissolved solids and clean the water.

Safe discharge

Once fully treated, the remaining wastewater is returned to waterways or land under strict consent conditions from Waikato Regional Council.

In Taupō, the water is pumped up to nearby farms where it's used to irrigate ryegrass, which we then sell as stock feed.

In Kinloch, the treated water is irrigated below the local golf course, where the nutrients help to grow lush green grass. This method prevents any nutrient leaching to groundwater or Lake Taupō.