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11 The annual review of drinking-water quality in New Zealand

11.1 Introduction

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. These are supplies that are contained in the Register of Community Drinking-water Supplies in New Zealand.29

The Review, which contains information about both the microbiological and the chemical quality of drinking water supplies, provides:

  • an overview of drinking water quality in New Zealand. This assists the Ministry of Health in evaluating the effectiveness of its policies and water supply management “tools” (eg, public health risk management plans) in improving the quality of drinking water and therefore minimising the risk of waterborne disease

  • for district health boards, an overview of drinking water in their district, so that they are better able to plan where their 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 their water supply.

The preceding discussions in this guide show that a large amount of information may be required in assessing the impact of a new activity on a water supply. Much of the information that is needed regarding the performance of a water treatment plant is already available in the Review and the Water Information New Zealand (WINZ) database (see below).

11.2 How the review is conducted

Information for preparing the review is collected by a national survey of water suppliers, which is undertaken through public health units. Water monitoring data collected by water suppliers, together with other information about the supply and its operation, are used as the basis for the review. The water supplier provides the raw compliance information, or a summary of it, to the drinking-water assessor, or health protection officer, who then assesses the supply’s compliance, or checks the water supplier’s compliance calculation30 if one has been done.

When the compliance calculations have been checked, a summary of the compliance information is forwarded by the drinking-water assessor to ESR using the WINZ database (see section 12). ESR prepares the Review from the summary information; detailed monitoring data are not included in the Review.

ESR prepares a draft of the Review and circulates it to the Ministry of Health and public health units for comment. Public health units provide water suppliers with copies of the information relevant to their supply for this to be checked. Once all checking has been carried out and any corrections needed are made, the final version is provided to the Ministry of Health for publication.

11.3 Information collected for the Review

Electronic forms are used to collect compliance information for the survey. The following information is collected by the survey – it may be of assistance in implementing the NES.

1. E. coli compliance at the treatment plant:

  • type of disinfectant used

  • whether E. coli monitoring was undertaken

  • number of E. coli samples taken

  • number of samples containing E. coli, but not the E. coli concentrations

  • whether the source was a secure groundwater

  • whether the treatment plant was compliant with respect to E. coli (this will have taken account of the above information, and other compliance criteria).

2. Protozoa compliance at the treatment plant:

  • treatment processes used to protect against protozoa

  • details about the type of filtration used (if used)

  • details about UV maintenance and management (if used)

  • whether the treatment plant was compliant with respect to protozoa (this will have taken account of the above information, and other compliance criteria).

3. Priority 2 chemical contaminants

The electronic form identifies the Priority 2 contaminants that have been assigned to each distribution zone and the treatment plants feeding that zone. (Many zones and treatment plants do not have Priority 2 contaminants assigned to them. See sections 3.4 and 8.1.)

The following information is collected for both the distribution zone and treatment plants for supplies to which Priority 2 contaminants have been assigned:

  • number of samples taken for each Priority 2 contaminant

  • number of samples in which the contaminant concentration was over 50% and up to 100% of the MAV

  • number of samples in which the contaminant was more than 100% of the MAV

  • maximum concentration of the contaminant found

  • whether monitoring at the treatment plant or in the distribution zone was compliant with respect to each assigned Priority 2 contaminant (this will have taken account of the above information, and other compliance criteria).

11.4 Information contained within the Review

11.4.1 National summary

The National Summary section of the Review identifies the key findings of the Review, discusses them and places them in the context of levels of compliance found in previous years, so that trends can be identified.

11.4.2 Summary statistics

National statistics and statistics for each local authority district are provided. These consider bacterial, protozoal and chemical compliance separately and within each of these categories statistics for local authority supplies, school supplies, and “other” supplies are provided. The numbers and percentages of water supply zones complying and the populations in these zones are presented, as are the reasons for non-compliance.

11.4.3 Supply-specific information

The summary statistics provide no detailed information about individual water supplies. Supply-specific information is contained in Appendix 1 of the Review. This appendix lists:

  • all registered supplies31 within each local authority district

  • the population of each distribution zone

  • whether the distribution zone complied with the DWSNZ with respect to bacteria (E. coli), and if not, the reasons for non-compliance

  • whether there was compliance with respect to protozoa for all treatment plants supplying the zone

  • the Priority 2 contaminants (chemical) for each distribution zone and any treatment plants supplying the zone, and whether there was compliance with respect to these contaminants

  • any changes in compliance status from the previous year for both bacterial and chemical contaminants.

The specific information contained in the Review’s appendix is of limited use for establishing how well treatment plants performed with respect to micro-organisms, for the following reasons:

  • The bacterial compliance information relates to the distribution zone only, not the treatment plant. Treatment plant compliance information is gathered during the survey of water suppliers, but is not published.32

  • With respect to protozoa, the appendix records whether there was compliance for all treatment plants serving each zone. Where there is more than one treatment plant serving a zone, an entry of “non-compliant” does not provide any information about which treatment plants were compliant. Moreover, there is no information provided about the nature of the treatment processes.

The supply-specific information in the appendix is more valuable for determining how the treatment plant performed with respect to chemical contaminants. Only distribution zones with Priority 2 contaminants assigned to them are listed in the appendix (no monitoring is required for other zones). The compliance status of each Priority 2 contaminant assigned to the zone and to treatment plants feeding the zone is given. Non-compliance because of an MAV transgression is identified. One complication with the interpretation of chemical contaminant information arises when more than one treatment plant feeds a distribution zone. In this situation it is impossible to determine which source water is responsible for any Priority 2 contaminants assigned to the distribution zone.

Compliance information gathered by the survey but not published, is held by a number of organisations, and can be obtained from them. Local authorities hold information concerning their own water supplies and public health units hold the information for water supplies in their jurisdiction. ESR holds the information for all water supplies, and can provide compliance information for water supplies within a particular regional council’s jurisdiction.

11.5 Availability of the Review

An electronic copy of the complete Review is available on the Ministry of Health website: www.moh.govt.nz/water.


29 The Register is maintained by ESR for the Ministry of Health in the Water Information New Zealand (WINZ) database (see section 12). Community supplies (see section 2.2.2) are registered by public health unit staff, once they become aware of a supply’s existence. It is likely that a substantial number of small water supplies are not registered, but it is very unlikely that supplies serving more than 500 people are unregistered, unless they are marae. The extent to which marae have been registered varies regionally.

30 This is a check on all the compliance requirements to see that they have been met. It takes into consideration such things as the frequency of monitoring, sampling locations, use of recognised laboratories, and appropriateness of corrective actions if they have been required.

31 These are the drinking water supplies recorded in the drinking water register maintained by the Chief Executive of the Ministry of Health.

32 This information can be obtained from ESR: Water Programme, PO Box 29-181 Christchurch, 8540.