Nature Calls: Help decide how Palmerston North treats its wastewater

We previously selected a preferred option and lodged consent

In 2021, we identified a best practicable option based on community feedback, technical assessments, and cultural input. A consent application based on that option was lodged in 2022.

We are reconsidering the approach because the earlier proposal was not affordable

By 2024, the estimated project cost had risen to more than $640 million. Long-term plan feedback showed that level of investment was too high for many households, so elected members asked staff to investigate lower-cost alternatives within a budget cap of $480 million plus inflation.

What changed nationally?

The government introduced new wastewater environmental performance standards in December 2025. These standards set clearer national expectations for wastewater treatment and discharge. Both options presented in this consultation are intended to meet those standards, while still requiring resource consent.

Read more about the background and timeline of Nature Calls on pages 2-5 of the feedback booklet.

Under Local Water Done Well reforms, Central Districts Water will become responsible for drinking water, wastewater and stormwater services across Horowhenua, Palmerston North and Rangitīkei from July 2027. That organisation is expected to take over responsibility for the Nature Calls project, including funding and delivery.

Council remains responsible for progressing the project until then. There are also proposed reforms to the Resource Management Act, which may introduce new environmental legislation in the future.

Read more about Central Districts Water and national water reforms on page 4 of the feedback booklet.

Cultural values and iwi input are part of the decision-making process.

Rangitāne, Te Tūmatakahuki and Ngāti Whakatere have provided input and advice throughout the history of Nature Calls. This has included hui, workshops with elected members, and ongoing collaboration about river conditions, discharge effects, mixing, nutrients, and river health.

This work will continue as the two options are further developed and assessed.

The earlier proposal from 2021 was estimated to cost more than $640 million. The options now being consulted on are lower cost, but still represent major long-term investment.

The figures shown in the options below are mid-range “P50” estimates. That means there is roughly a 50/50 chance the final project cost could be lower or higher.

Household impacts shown here are based on the current rating structure and are rounded. They could change in future depending on how Central Districts Water chooses to structure charges once it takes over responsibility for water services from July 2027.

All figures are shown in today’s dollars and exclude GST.

Read more about funding for Nature Calls on pages 4-6 of the feedback booklet.

Both options include adaptive management, which includes additional options we could use to reduce the effects of discharging treated wastewater on the river.

Instead of locking in one fixed solution for the next 35 years, adaptive management is a flexible approach that allows us to respond to new technology, changing environmental expectations, and any opportunities to improve how the system operates over time.

This could include:

• Diverting wastewater from the river at times
• Reducing inputs into the wastewater network
• Further treatment upgrades
• Technology improvements
• Riparian planting
• Wastewater reuse such as watering parks and reserves
• Resource recovery initiatives.

Adaptive management has been modelled separately from the main discharge options. It’s estimated to cost about $1 million per year over 40 years, with a rating impact of about $1 to $50 per year, depending on timing.

Read more about adaptive management on page 7 of the feedback booklet.

Since the budget cap was set in 2024, Council has carried out significant work to assess alternatives. Elected members have now narrowed that work down to two options.

The main differences are where treated wastewater would be discharged, how each option operates, and what each option costs.

Option 1: Keep the discharge at or near Tōtara Road after a major treatment plant upgrade

Cost: $292m + adaptive management ($1m per year for 40 years)

Under this option, treated wastewater would continue to be discharged into the Manawatū River at or near the existing outlet on Tōtara Road in Awapuni. Wastewater would be treated to a much higher standard than it is today before discharge, including:

• Reducing nitrogen from around 35 mg/L to around 4–5 mg/L
• Removing additional phosphorus
• Achieving extremely low bacteria levels
• Removing almost all solids from the water.

Why this option is different

This part of the river has a harder gravel and rock bed, so nutrient limits are stricter to stop excess periphyton growth – commonly associated with algae. Meeting those standards at low river flows would require continuous use of alum to remove extra phosphorus, which produces more sludge as part of the treatment process.

Option 2: Use two discharge locations depending on river flow conditions

Cost: $370m + adaptive management ($1m per year for 40 years)

Under this option, treated wastewater would be discharged to the Manawatū River at Tōtara Road when river flows are high, and below Ōpiki Bridge when river flows are low. Wastewater would still receive a very high standard of treatment before discharge, including:

• Reducing nitrogen from around 35 mg/L to around 4–5 mg/L
• Removing phosphorus using additional treatment, but less than Option 1
• Achieving very low bacteria levels
• Remove almost all solids from the water.

Why this option is different

This approach uses river conditions to manage effects. It avoids continuous alum use during lower flows by sending treated wastewater further downstream to a softer-bottom part of the river, but it requires a new pipe to Ōpiki and extra pumping infrastructure.

Read more about the two options on pages 8-11 of the feedback booklet.