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Oakura Water Treatment Plant

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Source of water
Groundwater: Aquifer (via two secure bores).
Surface water: Wairau Stream.

Present capacity
2,800,00 L/day (normal use 720,00 L/day)

Treatment

• Secure bores.
• Chlorination to provide residule disinfection in reticulation system.
• pH control and corrosion minimisation (lime).

Process description

The groundwater (minimum water age is 300 years) is pumped from a deep volcanic avalanche flow strata originating from the Pouakai Range. It is then piped to the water treatment plant where sodium hypochlorite disinfectant and lime slurry for pH correction and corrosion minimisation are added before it is sent to reservoirs for storage.

Disinfection is necessary to provide protection against contamination occurring in the reticulation, e.g. in the case of back flow. Production from the bores and dose rates are set automatically to maintain quality standards. The water is pumped to two 1.2 million litre capacity reservoirs.

To ensure security of supply a second bore has been drilled and commissioned. Having two bores provides backup to cover maintenance or pump failure, and can double the production when run in ‘dual mode’. Each bore alone can supply the average daily demand. However, it is preferable that each bore takes an equal proportion of the demand to minimise any possible adverse effects on the aquifers, as any over-pumping could permanently damage the aquifers and equipment.

The existing surface water source is maintained as a contingency in the unlikely case that both bores are unavailable. The surface water is treated via ‘automatic valve-less gravity’ sand filtration and gas chlorination.

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