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    Mei Te Vai Ki Te Vai    

Improving the water quality of the lagoons in Rarotonga and Aitutaki for the

benefit of our health, environment and economy

The purpose of the Mei Te Vai Ki Te Vai (MTVKTV) project is to improve the water quality of the lagoons in Rarotonga and Aitutaki for the benefit of our health, environment and economy.

Muri Lagoon is contaminated by sediments and nutrients that impact water quality, ecosystem diversity and its appearance. There are a number of reasons for this, including:

  • Wastewater

  • Current and historical agricultural land-use (forest clearing, fertiliser use and animal waste)

  • Development

  • Erosion.

The project has confirmed the source of the lagoon issues

MTVKTV has established a firm scientific understanding of the environment to ensure that any resulting new infrastructure is justified, robust and effective. Extensive scientific research has confirmed that on-site wastewater systems are the leading cause of Muri Lagoon’s poor health and resulting seaweed growths. However they are not the only cause, so additional changes will also be needed to restore the lagoon’s health.

The project also aims to:

Establish a clear direction for wastewater management in Rarotonga and Aitutaki

MTVKTV will develop a road map for wastewater management, including infrastructure design (collection, treatment and disposal) for Muri and Aitutaki, steps required to establish a Crown-owned water and wastewater authority, and information to help make investment decisions. The new authority will manage water and wastewater infrastructure in the long-term.

Identify and implement early actions to mitigate the condition of Muri and Aitutaki lagoons

MTVKTV identified early measures – dredging and riparian planting - to help reduce the rate of deterioration of the lagoons. These activities were completed in 2018.

Facilitate community and stakeholder involvement in the process

MTVKTV is also focused on providing the community with information to increase understanding of the environmental issues, and the role of the PMU and community in resolving them. The project is also actively seeking feedback from the community to inform its work.

Project Timeline

Project timeline


  • Launched the project and appointed specialist consultants

  • Engaged with the Muri community and key stakeholders through a series of workshops

  • Identified a long-list of possible early measures to help improve water quality at Muri Lagoon

  • Completed and published a literature review of Muri environmental studies

  • Prepared a summary of requirements for Environmental Impact Assessments needed to gain permits for sediment removal near Vai Te Renga Stream

  • Started an environmental monitoring programme. Used interim findings to design concepts for wastewater infrastructure for Muri.



  • Continued engagement with land owners, the community, and stakeholders

  • Completed a Draft Sanitation Master Plan

  • Prepared for establishment of To Tatou Vai, a Crown-owned water and wastewater authority

  • Launched To Tatou Vai website

  • Gained approval for early mitigation works - shore protection and beach nourishment

  • Completed environmental investigations in Muri and initial investigations in Aitutaki

  • Released Muri environmental investigation results and presented them to key stakeholders and the community

  • Identified an alternative disposal option combining ocean outfall and land-based treatment.



  • Environmental investigations peer reviewed by NIWA.


In early 2020, MFEM confirmed a reticulated wastewater system with tertiary-level treatment and land-based disposal is the preferred approach to the MTVKTV project. Next steps are:

  • Public information sessions on the draft Environmental Impact Assessment and draft design

  • Phase two of the social/cultural impact assessment

  • Begin detailed design of wastewater infrastructure

'Mei Te Vai Ki Te Vai' means 'from water to water' in Cook Islands Maori. 

Environmental Issues

Environmental issues

Our extensive environmental investigations have provided good quality data to help us identify and develop the best solution to the environmental problems in Rarotonga and Aitutaki.

The investigations looked at nutrient and sediment levels, where they come from, how they flow into the lagoon, and how they behave in the lagoon. This included examining groundwater flow paths, streams and discharges from land-based activities, including wastewater.

Preliminary investigations

In July 2017, we did preliminary investigations including:

  • using drones to map Muri Lagoon and its catchment area

  • establishing a new weather station

  • geophysical surveys

  • collecting water and sediment samples from the lagoon.

Main investigations

We started the main investigations in late 2017 across about 10 locations in the Muri catchment area. This work included:

  • using a drilling rig to install a permanent monitoring well in locations where ongoing monitoring is required

  • installing temporary wells using hand-held tools, in locations where only one-off sampling is required

  • installing stream monitoring stations near stream mouths and periodically sampling along streams and swamps.

The findings from the environmental investigations carried out by PMU has confirmed that nutrients from on-site wastewater systems is the leading cause for the water quality issues in Muri Lagoon.


From this report, there were three recommendations outlined:

  1. Implementing a more robust reticulated wastewater system to service the highly developed areas along the coastline.

  2. Protect and enhance swamps and the edges of streams.

  3. Regularly harvest the seaweed, to disrupt its self-feeding process and remove it as a source of nutrients.


The full report is available in the News and Publications section.

Investigations to inform treatment plant design and disposal method

Following the environmental investigations to determine the cause of the water quality issues in the Muri lagoon, further investigations were needed to inform the treatment plant design and location, and support the Cook Islands Government’s decision on the most suitable disposal method.

We have completed site investigations on Turangi land offered by Pa Ariki earlier this year, but we are yet to confirm a location for the potential wastewater treatment plant.


We have used this site as the ’basis for design‘ for a wastewater treatment plant in the Outline Environmental Impact Assessment (EIA). However, we are aware of and acknowledge that there are community concerns about using this Turangi site for a treatment plant.


We have designed the future wastewater treatment plant to be easily adapted for other sites, and we are actively engaging with community leaders and landowners to identify a site that’s more acceptable to the community.

We also engaged experts from UNSW to lead oceanographic and marine ecological studies, together with the Ministry of Marine Resources, to see how an ocean outfall can meet the standards and guidelines. Both land-based and ocean outfall options would need to meet stringent public health and environmental guidelines, and require ongoing monitoring and reporting once operating.

We are still looking for more offers of land in the Muri area that could be suitable for a wastewater treatment plant and/or land-based disposal.


For land based disposal, we are looking for a 15 to 20 hectares of land (this could be made up of smaller land parcels), with a slope no less than 5 per cent. For a treatment plant site, we need an additional two hectares (approx.) of flat land.


If you think you have suitable land to offer the project, or would like to register your interest in the public meetings, please contact the PMU on 28851 or email



We are working on an enduring solution for Rarotonga, while also progressing possible short-term measures to help improve Muri Lagoon’s water quality and reduce seaweed growth there.

Muri is our first priority because there is pressure from population density and tourism, and the lagoon environment is sensitive.


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Review of past monitoring from Aitutaki has shown that wastewater may be adversely affecting the water quality of the Aitutaki Lagoon. This is based on the extent of seaweed and algae in the lagoon, and on measurements of certain bacteria in the water.


The Mei Te Vai Ki Te Vai project is providing advice on minimising possible effects of wastewater on the water quality of Aitutaki’s lagoon. This includes improving policy, regulation and management of on-site wastewater treatment systems, and a summary of options for collecting and disposing of wastewater.

We completed initial environmental investigations in Aitutaki in early 2017. The findings from the environmental investigations in Rarotonga will further contribute to our understanding of the environment in Aitutaki.

To find out more, we are looking into the quality of groundwater in key areas in Aitutaki, investigating how this groundwater flows into Aitutaki Lagoon, and taking further measurements of the lagoon’s water quality.

Mei Te Vai Ki Te Vai is carrying out this work in Aitutaki alongside the Ministry of Marine Resources, building the capability of local staff to carry out the regular monitoring work, rather than frequent visits by staff from further afield. We are doing all work in close consultation with the Island Council and key Government agencies.

The full scope of work for the project in Aitutaki is still being finalised.

Restoring our lagoons

Restoring Our Lagoons

Completing new wastewater infrastructure will take time, and it will also take time for water quality in Muri Lagoon to improve. This is why we are planning early measures alongside a new wastewater system. Early measures are actions we can implement in the short term to help alleviate some of the issues.

We investigated a range of potential early measures, and are progressing the following:

Sediment removal (dredging)

One of the factors contributing to seaweed growth is the presence of sediment from the land that has washed into the lagoon through streams. Together with the community, we have identified an opportunity to remove some of these sediments, which also block the flow of water within the lagoon.

We received consent from landowners and property owners and National Environment Service (NES) approved our Environmental Impact Assessment for sediment removal in the Vai Te Renga Stream area (near Pacific Resort). We used the sand we removed to replenish the beach near Nukupure Park.


We based our decision to dredge in this area on scientific surveys that showed how sediment removal and reinstatement of reef gaps would impact the lagoon’s water flows and salinity. When planning sediment removal we have also had to balance the benefits of dredging with the potential environmental impact of dredging work in the sensitive lagoon environment.

We completed this work in March 2019. Thank you to the landowners and the property owners for their support of this work.

Riparian planting

We have worked closely with the Ministry of Agriculture, Ridge to Reef team and others to progress the planting around streams. This is to reduce the sediment and nutrients entering the streams and ending up in the Lagoon.

We have planted after the proposed sediment removal to remove build-up and increase water flow in the Lagoon. Initial planting efforts focused on the Vai Te Renga Stream (near Pacific Resort) and the beachfront at Nukupure Park to help alleviate erosion. 

Protecting our lagoons

Protecting Our Lagoon

Nutrients from on-site wastewater treatment systems is the main cause of environmental issues in Muri Lagoon, so designing a new reticulated wastewater system for the Muri area is a key part of the MTVKTV project.

The purpose of the new infrastructure is to collect wastewater (from toilets, sinks and other drains) from properties and feed it through a network of pipes, pump stations and other infrastructure to a single point for treatment and then disposal. This will treat wastewater on a larger scale and reduce the impact of wastewater on the natural environment.

Wastewater infrastructure

Wastewater Infrastructure
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We have been developing, with input from the community, options for a new wastewater system that’s sustainable, and supports a healthy and prosperous future for the people of Rarotonga.

A Concept Design is the first step to designing the wastewater infrastructure. The concept design stage looks at technical issues and options at a high level to develop the most appropriate approach.

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As part of the concept design work, we considered a wide range of potential options for wastewater disposal. Not all options are suitable in the context of the Cook Islands, and not all options are equal. We have identified two possible ways to dispose of treated wastewater in Rarotonga – either onto land, or into the ocean.

You can read more about these two disposal options in the Options Guide, available from our Publications page.


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Community feedback to-date indicates preference for a land-based system, but there have been very few offers of suitable land to make this option viable. 


Whether land is suitable for treated wastewater disposal or not depends on a combination of things such as slope, distance from the treatment system, soil type and rainfall. The PMU is very keen to hear from anyone who has land in the Muri area they can offer to the project.


In response, the team is currently investigating whether a combined ocean outfall and land-based system could be a third option, as a way to progress land-based treatment within a much smaller footprint. This would enable the benefits of using a nature-based final treatment stage to be realised, while also catering for wastewater volumes.

We have developed a map (shown below) showing the area in which we need land.

  • If land disposal is chosen, we'll need two parcels – about 2 hectares/5 acres for the treatment plant, and another of at least 16 hectares/39.5 acres for disposal of treated wastewater to land. The land for disposal would need to be within about 4km of the treatment plant.This is just to service the Muri area - additional land would be required in future to service other areas.

  • If ocean disposal is chosen, only one land parcel of about 2 hectares/5 acres will be required, for the treatment plant and pumping station to send treated wastewater to an ocean outfall.

  • If a combined system is chosen, we will need two parcels - one for the treatment works and pumping station, and one of about 1.5 hectares/3.7 acres for a trial disposal of treated wastewater to land. The land for disposal would need to be within 2.5km of the treatment plant.

We have presented concept design options to the Cook Islands Government for their consideration. The Government will choose one of these options to progress to detailed design for Muri. This option may also be used elsewhere around the island.

Detailed design can begin after the Government has selected a preferred design option. The detailed design stage develops the details needed for construction.

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Above: Area of potentially suitable land for  Muri wastewater treatment infrastructure

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Frequently asked questions

What is wastewater?

Wastewater is all the water that is flushed down toilets, sinks, showers and other drains from households and commercial premises.

What is wastewater infrastructure?

Wastewater infrastructure is the network of pipes, pump stations, treatment plants and disposal sites that collect, treat and dispose of wastewater.

What is wastewater reticulation?

A wastewater reticulation system is the network of pipes, pump stations and other infrastructure that collects wastewater from households and commercial premises, and transports it to a single point (off-site).


What is wastewater treatment?

Wastewater treatment is when raw wastewater undergoes various processes to reduce the number of pathogens and nutrients in the water. Depending on the design of the wastewater system, treatment can be undertaken to various levels (primary, secondary and tertiary treatment). 


What is wastewater disposal?

Disposal can take many forms, but broadly you can discharge to land or to the marine environment. 

What is an ocean outfall?

Ocean outfall involves dispersing treated effluent deep into the ocean beyond the reef, using a special ‘diffuser’. The ocean currents disperse and dilute the treated wastewater, and the sea life consumes any remaining nutrients and organic matter it contains.

Read more about ocean outfall here.

What is land-based disposal?

Land-based disposal involves either spraying treated wastewater onto land using an irrigation system, or drip-feeding it beneath the soil using irrigation pipes. The PMU has concluded that the sub-soil drip-feed option is more suitable for Rarotonga.

Read more about land-based disposal here.

Why were more investigations required?

The first step towards restoring the health of the lagoons is confirming what’s impacting its water quality.

Our literature review of the environmental studies of Muri Lagoon revealed that previous studies did not confirm the factors contributing to the water quality of the Lagoon. This meant further investigation was necessary.

Our additional investigation work built on the results of the existing studies and closed the gaps in information. They provide results and methodology that can also be used for water quality assessment, monitoring and management in other parts Rarotonga and the Cook Islands.

Have you decided to dispose of wastewater into the ocean?

No, we have not. Alongside ocean disposal, we are also evaluating and preparing information on land-based wastewater disposal, to enable Government to consider both options before deciding on a preferred method.

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