Water supply grading

Quality standards for drinking water are set by the Ministry of Health (MoH), through the Drinking Water Standards for New Zealand. Each year the Ministry publishes a grading for every public water supply. Gradings are based on the drinking water standards and indicate how safe each water supply is from contamination.

The MoH grading system has two parts:

1.  A grading for the source of water and the treatment plant ("A1" to "E"). This relates to the measures taken to limit contamination of the water source and to remove any contamination that is present, by treatment. It is a rating of how safe the water is after treatment, but before it enters the distribution system.

2.  A grading for the distribution system ("a1" to "e"). This is based on the risk of water becoming contaminated within the local supply pipes, and the procedures in place to minimise the risk of unsafe water to consumers.

The grading range from completely satisfactory ("A1" or "a1") to completely unsatisfactory ("E" or "e") .

Our source and treatment plant gradings are:

  • A1 - Te Marua
  • A1 - Wainuiomata
  • B - Waterloo
  • A1 - Gear Island

Our bulk distribution system gradings are:

  • a1 - Wellington Region Upper Hutt Porirua
  • a1 - Wellington Bulk Lower Hutt
  • a1 - Wellington Bulk South Wellington

Our goal is to have at least an "A1'' grade for the water leaving each of our water treatment plants, where that is consistent with the requirements of our customers.

A water supply can't be graded higher than "B" if chlorine disinfectant isn't used in the distribution system. Waterloo currently has a "B" grading because when it was last graded it did not supply chlorinated water, which it now does. The grading of Waterloo is expected to change during the next grading round. For more information on the chlorination of Waterloo water, check out this page

Each year the Ministry publishes the Register of Community Drinking-Water Supplies, which lists the water supply grading for every community in New Zealand. To check the grading for your area, click on MoH water supply grading.