Wastewater is anything that goes down a drain inside your home or business – from your kitchen, to your laundry, to your bathroom.

Watch: Find out what happens once the water goes down your drain.

Every year, up to 12.9 billion litres of wastewater is collected from 31,700 homes or business around the city.

Forty pumps move wastewater along a 405-kilometre network of pipes, which we are responsible for maintaining and upgrading. To put that into context, our network would stretch from Palmerston North to Hamilton if the pipes were laid end-on-end.

Our wastewater treatment plant then removes contaminants so the end product meets safe and legal quality levels for discharge to the environment. You can learn more about the process below.

Don’t flush wet wipes down your toilet

The only thing that should ever be flushed down your toilet is the three Ps – pee, poo, and (toilet) paper.

Wet wipes, paper towels, and tissues are highly absorbent and don't break down well in pipes – even ones that claim to be flushable. They cause blockages when they mix with fats, oils, and grease that have been poured down your sink.

We aren’t responsible for unblocking pipes on private properties, so if yours get blocked with wet wipes you’ll be required to cover the cost of a plumber.

How to reduce your wastewater

The average person in Palmy creates about 210 litres of wastewater each day.

Here are some easy thing you can do each day to reduce wastewater at your whare:

  • Save 6 litres by turning off the tap while you brush your teeth
  • Save 90 litres by reducing your shower from 10 minutes to five minutes
  • Only put your washing on when you have a full load
  • Use the half flush on your toilet
  • Save 15 litres by fixing a leak
  • Save 6 litres each minute by switching to a low flow showerhead – and cut the cost of your power or gas bill
  • Wash your vegetables in a sink of water rather than running the tap
  • Wash you dishes by hand rather than using a dishwasher

What makes up domestic wastewater?

  • Bath (1.7 per cent)
  • Dishwasher (1.7 per cent)
  • Leaks (3.2 per cent)
  • Tap (14.6 per cent)
  • Toilet (20.4 per cent)
  • Washing machine (26.1 per cent)
  • Shower (32.3 per cent)

Trade waste

Around 12 per cent of wastewater volume comes from trade waste, which is the liquid and material discharged by business. This includes solids, fat, oil, grease, solvents, emulsions and chemicals that come from industrial or trade processes. 

We have about 500 trade waste customers, which are controlled through a permit system. This is because trade waste can contain substances that are detrimental to the wastewater system, treatment plant process and the environment.

By comparison, residential and other commercial sources make up 88 per cent of our wastewater volume.

Visit our trade waste webpage for more information.

Rain entering the wastewater network

Rain and groundwater can sometimes get into our wastewater pipes from illegal house connections, such as incorrectly connected stormwater systems, and broken sewer mains. You might also hear this referred to as inflow or infiltration.

A common point of entry for stormwater into the wastewater network is through a gully trap. Council is actively trying to reduce inflow and infiltration by regularly monitoring our network with CCTV cameras. You can read more about this on our stormwater page.

Bio-gas generator

We have a bio-gas generator located at the Totara Road Wastewater Treatment Plant, which supplies power to the treatment plant and Awapuni Resource Recovery Centre.

Methane gas is captured from the retired Awapuni Landfill – decommissioned in 2001 – and from sludge digesters at the wastewater plant. The digestors use a biological process to break down sewage sludge. The process is designed to capture the bi-product – methane gas – before feeding the gas into the generator as a fuel source to produce electricity.

Not only does this prevent methane gas from polluting the environment, but the electricity produced offsets about 40-50 per cent of the total annual power requirements for our wastewater plant.

In the year to March 2021, the bio-gas generator made 1,992 Megawatts an hour, while consumption at the treatment plant was 1,885MWh. That means 107MWh was sold back to the grid.

Since February 2018, we have made $11,600 from selling electricity back to the national grid.

Treating and discharging Palmy's wastewater

Diagram showing the process for treating Palmerston North wastewater before it is discharged into Manawatū River.

When it arrives at our treatment plant in Tōtara Road, we filter things in our screening room that shouldn’t have gone down a drain – like wet wipes, condoms and tampons. These need to go in your bin.

The wastewater is then pumped with air to remove grit or sand, before passing onto our sedimentation tanks. Here, the solid material sinks and the cleaner material moves on. Solid material isn’t just poos – it includes fat and oil and food scraps from your sink.

It then goes to lagoons where air is pumped into the water allowing microorganisms to grow and eat any remaining solid material.

We remove phosphorus from the water and blast it with UV light. By the time the water reaches our small wetland, 99.9 per cent of bacteria has been removed. The water passes through the wetland into the river after about four days of treatment.

The remaining solids stay on site for 20 days, where bacteria help break it down before it’s removed offsite.

Nature Calls – managing our future wastewater

Nature Calls focuses on how we treat and discharge our wastewater for the next 30 to 50 years.

Palmy is growing and our existing system will need to as well to meet the demand of our future population. Improvements to accommodate increased wastewater flows as our population grows will be a key part of our capital investment and work programme.

To learn more, visit our Nature Calls webpage.