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Improved water will soon flow through new water supply system

Updated: Nov 24, 2020

The Cook Islands Government has instructed the Te Mato Vai Stage 2 contractor McConnell Dowell to begin commissioning the new intake water supply systems. Currently the public water supply is still connected to the old intake infrastructure. Now McConnell Dowell will begin connecting the public water network into the newly constructed intake water treatment systems. Water will begin to flow through the new system within the next month - intakes are being connected one at a time, starting with Matavera.

Ongoing engagement with affected landowners and local leaders will continue alongside the commissioning work. The new system will be disinfected using chlorine before being connected, but no chlorine will be added to the drinking water supply at this stage.

The Government is committed to continuing the current consultation with affected parties, and believes commissioning Te Mato Vai will enable better-informed decisions about the long term future of Rarotonga’s public water supply. The Government is obliged to prevent additional significant costs, and job losses that will result if Te Mato Vai is further delayed.

When connected, the public water supply will go through all steps of the new treatment system except chemical disinfection (chlorination) of the water supply.

The water treatment will be a three-step process:

1. Removing larger solids (such as dirt and leaves) from the water. Called ‘sedimentation’ this involves holding the water in a tank and letting solids sink to the bottom, so cleaner water can be taken from the top and into the next treatment step.

2. Removing the smaller particles, including harmful protozoa that can cause diseases such as Giardia. Called ‘coagulation/flocculation’, this involves slowly mixing a ‘coagulant’ into the water, which makes small particles stick together and settle at the bottom of the tank.

3. Filtering to further clean the water. This process uses sand to further remove harmful protozoa and other contaminants.

The fourth step, disinfecting the water to kill harmful viruses and bacteria and keep the pipes clean, will not be commissioned at this stage. This means that while the water quality will be significantly improved, it will not be considered safe to drink without additional treatment (such as boiling) to kill viruses and bacteria.

The new system also includes improved water storage, with new tanks able to hold up to 15 million litres of water. During the drought periods, these tanks are large enough to supply approximately two days of water to Rarotonga, depending on how much water the community uses.

The Government considered the views of intake landowners, local leadership and the wider community before deciding to approve both disinfection of the new infrastructure and use of the ‘coagulant’ chemical, polyaluminium chloride (PACl).

PACl plays a key role in cleaning water, but is different from chlorine, which is used for disinfection. PACl is a ‘coagulant’ used in the water treatment process to remove small particles of dirt and other contaminants, including harmful protozoa that can cause diseases such as Giardia. Coagulants are essential when treating water that comes from streams, because stream water contains dirt, leaves and other contaminants. PACl is removed from the water before it enters the pipe network, and the used PACl will be disposed of responsibly.

PACl will initially be introduced for a trial period. The coagulation process will be closely monitored during the trial. The monitoring reports will be used to inform Government and landowners’ views on longer term PACl use.

The new infrastructure will be disinfected using a one-off ‘flushing’ with chlorine, before the water supply is connected to households. After flushing, the chlorinated water will be removed and disposed of responsibly. No chlorine will be added to the water supply at this time.

The Government confirms that the Te Mato Vai Stage Two project holds all the necessary National Environment Service (NES) permits for construction and commissioning

Until a decision is made on the preferred water supply disinfection method, To Tatou Vai and Ministry of Health will continue to test the public water supply for bacteria and monitor the community water stations to protect public health.

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