Treatment plant operators undertake the day-to-day running of water treatment plants and are therefore a source of detailed information about the operation of their water supply. Information from treatment plant operators is best obtained through contacting the water supply manager at your local authority.

1 Treatment plant operators

If the water supply is not operated by a local authority, a drinking water assessor at the public health unit may be able to put you in touch with the water supplier, who in turn can give the operator’s details if the treatment plant operator is a different person from the water supplier.

Depending on their level of training and experience with the treatment plant, the treatment plant operator may be able to provide the following information relevant to making decisions on
the NES:

  • the monitoring undertaken at the treatment plant, which may include samples taken for compliance purposes (eg, E. coli) and operational monitoring of parameters, such as turbidity and acidity/alkalinity (pH)20

  • advice on how the treatment plant copes with increases in turbidity in the source water, and the level of turbidity increase that might be tolerated without compromising the plant’s ability to comply with the DWSNZ

  • activities in the catchment that contribute to the contaminants that must be removed by the treatment plant

  • the degree of removal of common chemical contaminants, such as iron and manganese, providing they have already been identified as a problem and there are treatment processes in place to remove them

  • how the flow rate or level of the source water at the abstraction point affects the finished water quality.

It will be more difficult for treatment plant operators to estimate their treatment plant’s ability to remove a new contaminant: the treatment may not have been specifically designed to remove it, and they may not previously have needed to carry out such treatment. For example, if cyanide contamination is a possible consequence of a proposed catchment activity, the operator may be unable to estimate the extent to which existing treatment processes will remove this contaminant. In such situations, an independent consulting engineer could be asked for advice on the likely extent of removal. For applications where this is necessary, this should be assessed as part of the assessment of environmental effects (AEE). If this information is not provided, it should be officially requested via a section 92 letter.

2 Water Information New Zealand

Water Information New Zealand (WINZ) is a national database of information on water supply management and water quality. It is maintained by ESR on behalf of the Ministry of Health. It provides water supply information, including the characteristics of supplies, public health grades, and compliance with the DWSNZ. Both permanent (location and details of the supply system) and transitory (compliance with DWSNZ grading) data are stored in the database.

WINZ software is developed and maintained by the Water Information Systems group of ESR. The group distributes software updates to water suppliers, district health boards and other organisations that may be running WINZ.

Three levels of WINZ have been developed to meet the specific needs of different organisations involved in the management of drinking water supplies. Explained in more detail below, these are:

  • WINZ for water suppliers

  • WINZ for district health boards

  • National WINZ.

WINZ for water suppliers

Not all water suppliers use WINZ. Those that do are provided with a version that contains information relevant to their water supply only. From the supply-specific information, the software is able to calculate monitoring requirements and provide a suggested sampling schedule.

Once monitoring data is generated, the water supplier can store it in WINZ. The software will determine the compliance status of the supply when sufficient information is available. Events such as transgressions,21 and actions taken in response, can be recorded and stored in WINZ. The software generates warnings of the need to take corrective actions in the event of a transgression.

WINZ for district health boards

All district health boards use a version of WINZ that is essentially the same as the version provided to water suppliers, but with some additional functions. Individual suppliers receive information about their supply only; district health boards have access to database information about all supplies in their district.

The district health board collects compliance information from water suppliers and uploads a summary of the information to National WINZ, maintained by ESR. This is then used for preparing the annual Ministry of Health publication on water quality on New Zealand drinking water supplies, the Annual Review of Drinking-water Quality in New Zealand (the Review).

National WINZ

National WINZ is maintained by ESR on behalf of the Ministry of Health. The database stores high-level information uploaded from public health units; it also shows supply details and public health grading information. The National WINZ data is used for:

  • compilation of Ministry of Health publications – the Register of Community Drinking-water Supplies and Suppliers in New Zealand and the Review

  • analysis of water supply information to help the Ministry of Health develop policy

  • research requiring national-level information about water supplies and compliance, or information about specific water supply systems (eg, the treatment processes in use).

WINZ and NES implementation

Two types of information contained within WINZ will be relevant to implementing the national environmental standard: supply details and compliance information. Drinking water assessors in public health units are a useful first point of contact for obtaining and understanding information in WINZ about individual water supplies.

Supply details

When a water supply is registered, each component of that supply is given a unique identification code. Some basic details about each supply component are stored in WINZ. For treatment plants, these details include the grid reference of the treatment plant and the regional authority in which the plant is located. Details about treatment operations and treatment chemicals used at each treatment plant are also retained.22

Compliance information

Compliance information can help establish how well a water supply’s treatment plant is functioning, and therefore how well it will deal with new contaminants or increased levels of existing contaminants.

Drinking Water for New Zealand website

The Drinking Water for New Zealand website ( is managed by ESR for the Ministry of Health. This includes valuable information about the quality and safety of New Zealand’s drinking water.

3 Annual review of drinking water

Each year, ESR prepares the Annual Review of Drinking-water Quality in New Zealand (the Review) for the Ministry of Health. The Review contains information from all registered community water supplies and provides:

  • an overview of drinking water quality in New Zealand, which assists the Ministry of Health to evaluate the effectiveness of its policies and water supply management tools (eg, public health risk management plans) in improving the quality of drinking water, therefore minimising the risk of water-borne disease

  • an overview for district health boards of drinking water in their district so they are better able to plan where efforts for improving drinking water quality should be directed

  • detailed information on the performance of individual water supplies for those wanting to know about the quality of a supply.

Much of the information needed to assess the effects of a resource consent on the quality of drinking water and, in particular, the performance of a water treatment plant, is available in the Review and WINZ.

Note that there can be a considerable delay between the end of the monitoring year and public release of the Review. This is because substantial cross-checking of data is required by drinking water suppliers, public health units, ESR and the Ministry of Health to ensure that both individual supply information and the resulting national summary are accurate. This can lead to delays of a year or more.

4 Ministry for the Environment

The Ministry for the Environment has prepared a database to help implement the NES. The information in this database has been obtained from ESR, which maintains the WINZ database on behalf of the Ministry of Health.

This database is compatible with Geographic Information Systems (GIS) and has been sent to all regional councils. It includes drinking water source abstraction points, drinking water treatment plants, and some information on drinking water supply compliance with the DWSNZ. This will help councils determine whether drinking water from an individual supply meets the health quality criteria. The database is in Microsoft Access format and is intended to be integrated with existing GIS systems at regional councils.

This database is provided only to regional councils to assist with their regulatory functions under the NES. Permission has been obtained from the Ministry of Health to supply this database to regional councils for this purpose. The Ministry for the Environment distributes the database to regional councils. Wider distribution of the database is not permitted.

The Ministry for the Environment cannot release its database, which is based on WINZ data, until the most recent annual Review is publicly released by the Ministry of Health (see section 3 above). This is because earlier release of the database would mean a public release (albeit limited) of data that has not yet been released by its owner (the Ministry of Health). Councils will need to continue using the previous year’s database until the Ministry of Health has published the annual Review, and has thereby publicly released drinking water quality compliance data nationally.


20 Treatment plant monitoring information is usually primarily for finished water and the plant operator’s parameters. Source water monitoring is usually sparse, and for most plants is undertaken only sporadically (if at all).

21 Transgressions are exceedances of the MAV for a determinand; see Appendix 1 for more information.

22 Types of contaminants the treatment plant should be able to reduce in concentration can be identified from knowledge of the treatment processes in use. However, WINZ should be used for this purpose as a first approximation only. Check with the water supplier to confirm which processes are operational, and the degree to which treatment plant processes will reduce concentrations of expected contaminants.


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