Drinking Water for New Zealand

Managed by ESR for the Ministry of Health.         Data extracted from the National DWO Database.

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Supply Structure Explained

Use this page to understand the structure and details as listed against a particular supply. The Explain Compliance page may also be helpful.


The registration details for over 700 networked drinking-water supplies can be viewed on this website. Details are extracted weekly from the National WINZ (Water Information for New Zealand) database.

The simplest supply for a community has a water source, a treatment plant (if treated), and a single distribution zone (ie the pipe network which delivers the water to your gate.) This would be structured in the Register as:

Supply 1

      Zone 1

            Plant 1

                  Source 1

This structure represents the small community in the diagram following.

Larger towns and cities often have several sources, plants and zones, all connected in various ways (move your mouse over the picture to see an example). As more parts are added, the Register entry for a supply lengthens, but the same line-by-line pattern is used. That is, for any zone you see listed, it receives water from the plant or plants listed under it, and the plants in turn are fed by the sources listed under them.

Supply schematic

The registration details include population and, where supply population exceeds 500, a Public Health Grading. This consists of a single grading for each treatment plant (eg B) and a combined grading for each distribution zone (eg Ba).

What are Zones and Plants?

Distribution Zone: This is all or part of the town or community that receives similar quality water from its taps. If different parts of town have different water sources or conditions, then the supply will be divided into two or more zones. The emphasis is "each zone has similar quality water throughout" and therefore can be evaluated for compliance with the Standards.

Treatment Plant: A zone receives water from one or more treatment plants, which in turn receive water from one or more water sources (rivers, lakes, groundwater, etc.) If there is no physical treatment, for example with some groundwaters, a nominal treatment plant is still defined so this and other details can be recorded against its name.

The Public Health Grading

The grading rationale and process is explained more fully on the Public Health Grading of Supplies page, but the meaning of the actual grades is summarised here.

Note: currently there is no national requirement for supplies to be graded, but the option remains for each supplier.

Distribution Zone Grades

Zone grading (a1 to e) is based upon the microbiological and chemical quality of the water, along with the condition of the reticulation system and the quality of its care, etc. A zone grading should always be considered with the accompanying plant and source grading.

a1       Completely satisfactory, negligible level of risk, demonstrably high quality
a Completely satisfactory, extremely low level of risk
b Satisfactory, very low level of risk
c Marginally satisfactory, moderately low level of risk.
d Unsatisfactory level of risk
e Unacceptable level of risk
u Not yet graded. (Not yet required if less than 500 people)

Source and Plant Grading

Plant and source grading is based primarily on the likely health risks to the community arising from bacteria, protozoa (Giardia and Cryptosporidium) and chemical substances in the source water, and how effectively the treatment plant can act as a barrier to such contaminants passing through to the reticulation.

Possible gradings are A1 (best), then A to E. As well as appearing against each plant, each zone inherits the plant grading from the worst plant providing it with water.

A1       Completely satisfactory, negligible level of risk, demonstrably high quality
A Completely satisfactory, extremely low level of risk
B Satisfactory, very low level of risk when the water leaves the treatment plant.
C Marginally satisfactory, low level of microbiological risk when the water leaves the treatment plant, but may not be satisfactory chemically.
D Unsatisfactory level of risk
E Unacceptable level of risk
U Ungraded

Local Authority

The local authority shown is the territorial local authority for the geographic area within which the supply is located. While they also own many supplies, others are owned privately or run by public or community organisations. Therefore, the supplier is shown as a separate line.



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