Drinking Water for New Zealand

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

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NZ Processes

New Zealand Processes for Managing Drinking-Water Quality

This is a simplified overview of how drinking water quality in New Zealand is managed and assessed.
It is not an official description, nor a definitive one.
If it is broadly helpful though, it has served its purpose.

For that definitive understanding, the viewer should consult the Ministry of Health website, the drinking water Standards and the Health Act themselves, or consult with Drinking Water assessors in the public health units of district health boards.

Who looks after your water?

Nationally, the Ministry of Health, through the provision of standards, guidelines and other tools, ensures that an appropriate infrastructure is present in New Zealand to support the provision of clean and safe drinking-water to communities. Underlying the standards and processes is the Health (Drinking-Water) Amendment Act 2007.

At the local level, the typical supply on this website is owned by a territorial local authority (TLA) such as a district or city council. They extract the source water, run the treatment plant to remove risks or contaminants, and pipe the water to your door. Under the Drinking-Water Standards for New Zealand 2005, they are expected to manage the supply, guard against risk, and test the water regularly to demonstrate that it is safe. If you are unhappy with your water supply, your first step should be to contact them.

The Ministry of Health does not check on the local authorities directly. That function is performed by Drinking Water Assessors (DWAs), who are authorised officers with public health experience and qualifications in drinking water. DWAs are employed within the Public Health Units(PHU) of District Health Boards.. Each PHU oversees the suppliers in its area and ensure (audit) that they maintain appropriate water quality. You can discuss health aspects of your drinking-water with a DWA if you have concerns. DWAs also report to the Ministry so that a national picture (such as the Annual Review) can be attained of the state of all networked drinking-water supplies.

What are the components of a water supply system?

See an explanatory picture

The simplest water supply is just a well with a pipe from it, or a pipe from a river or lake, perhaps with a pump and storage tank. More commonly though, as a population increases, a treatment plant is present to remove actual or potential contaminants and ensure that the water delivered is safe to drink. The most common treatment is chlorination, where a chemical compound is mixed with the water to kill any bacteria from the source. This treatment will also maintain some degree of residual "resistance" to any subsequent bacterial entry to the water while it is in the pipework. Other treatment processes include coagulation (making fine particles drop out), filtration and the removal of other contaminants. Removal of cloudiness is important because chlorination is not as effective otherwise.

The water is transported to users through a network of pipes, known as the reticulation or distribution system. In larger cities, some suburbs may be supplied differently from others. Additional pumping may be required to suburbs on the hills, or the city may be subdivided, with one plant supplying to one part but not to another. For a complex situation like Dunedin City, at least eight areas can be identified as having water different to their neighbouring suburbs.

The different components of a water supply are listed in the supply structures in a way that indicates how they are connected. Here is a brief summary of the terms used:

Community: The people served by the supply.

Zone: (or Distribution Zone) That part of the town or community receiving water of similar quality. For a small supply, that means "everywhere". For larger supplies, it may be only part of a town or city. By definition, parts receiving different water will be in different zones.

Plant: The treatment plant supplying the water. In some situations where no treatment is given, a nominal plant is defined as where the water is pumped from or merely gathered together. In others, the treatment plant will have highly technical operations with extensive automated control and monitoring of water quality. Larger supplies may have multiple plants.

Source: The river, groundwater, or other source from which the water is taken. About half of New Zealandís drinking-water is pumped from the ground, with the remainder coming from surface sources. Larger supplies may have multiple sources.

In the supply structures listed on this website, each of these components is on a separate line and each component has its own code, which is unique in New Zealand. The lines are ordered so that you can see which plants and sources supply each zone.

What are the major water quality concerns?

Chemical contamination of New Zealand supplies is always a risk, but usually it is a very small one. Most chemicals mentioned in the Drinking-Water Standards for New Zealand 2005 specify levels likely to cause adverse effects only after prolonged periods of exposure, so, with some exceptions, chemicals are not the main area of concern unless there is a major chemical spillage.

Throughout the world (and New Zealand is no exception) by far the most common problems arise from microbiological contamination of the source waters. Animal, bird and even human effluent, introduced in one way or another upstream from a water supply, can make that water unfit for consumption. Bacteria have always been of major concern, while protozoa such as Giardia and Cryptosporidium are increasingly being highlighted as causing ill health through drinking-water.

There are two ways of minimising the risk from these microbiological contaminants:

  1. Keep the source as clean as possible, by protecting the catchment and minimising the possibility of contamination.
  2. Treat the water to destroy any contaminants introduced.

The most successful approach is to use both of these, and to regularly monitor the water quality to demonstrate that any risks are being controlled. Good systematic and ongoing risk management is important.




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