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Our treatment plants
Te Pūnaha Maimoatanga Wai o Ōākura

Okato Water Treatment Plant

Source of water

Mangatete Stream

Present capacity

1,00,000L/day (normal current flow 430,000 L/day; peak 765,000 L/day).

Treatment

  • Bank infiltration gallery.
  • Cartridge filtration.
  • Ultraviolet disinfection.
  • Disinfection (chlorination).
  • pH adjustment (lime).

The water treatment process

Water from the Mangatete Stream is drawn through an infiltration gallery. The infiltration gallery consists of a slotted pipe buried in the stream bank. The stream bed and filter material placed on top of the pipe act to filter gross solids from the raw water before it enters the plant. Water flows by gravity to the treatment plant where the following multi-barrier process occurs.

At the treatment plant, water passes through a two-stage microfiltration system consisting of two banks of cartridge filters run in parallel to remove fine particles and protozoa oocysts (e.g. giardia). The first bank of cartridges is one micron nominal, and the second bank is one micron absolute.

After filtration, water passes through an ultra-violet sterilisation unit which provides an added barrier against protozoa contamination (and also provides primary disinfection).

Chlorine gas and hydrated lime are added to the water leaving the ultra-violet units. Chlorine is added as a disinfectant to deactivate any micro-organisms that might be present in the water that is distributed to the reservoirs, and as a safeguard against further contamination of the reticulation system.

Lime is added to raise the pH of the water to 7.6, making the acidity/alkalinity level healthy for consumers and non-corrosive to reticulation and household plumbing.

The water passes to the 1.2 million litre capacity reservoir.

Page last updated: 11:22am Thu 27 August 2026

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06 759 6060 enquiries@npdc.govt.nz
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84 Liardet Street
New Plymouth

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