Drinking Water for New Zealand

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

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Drinking-Water Standards for New Zealand

DWS 2005 cover 2008The current Standard is the Drinking-Water Standards for New Zealand 2005 (revised 2008). You can link to the latest official copy from our list of Ministry of Health documents or click the picture here.

Compliance with the Standards

For a drinking-water supply, compliance is determined by considering how the quality of the water compares with the requirements of the Standards. To meet these Standards, a monitoring process is usually required.

Non-Compliance or Transgression. What's the Difference?

Monitoring is the process of taking samples from a water supply at specified intervals to measure potential contaminants. Good systematic and ongoing management is important.

If an individual sample result fails to meet the maximum allowable value (MAV) or some other requirement, it is said to be a transgression. In some cases a few transgressions are allowable.

Compliance with the Standards is not based on the results of a single monitoring sample, but is an overall measure of whether the Standards requirements are met for a full 12 month period:

Compliance can include evaluation of aspects such as:

How much monitoring is necessary?

The amount of monitoring required is specified in the Drinking-Water Standards for New Zealand 2005. The standards speak about "determinands", which are chemical substances, microbiological organisms, or some other characteristic of the water that can be measured, "something for which you can test".

The standards divide all determinands of public health significance into four classes according to the priority with which they should be measured. This avoids unnecessary monitoring. Of the four classes, only determinands in the Priority 1 and 2 classes require measuring, but the others have been defined in case they are required in the future.

What are Priority 1 determinands?

The determinands with the highest priority for monitoring, appropriately called "Priority 1 determinands", must be measured in all drinking-water supplies. These are currently micro-organisms which are of public health significance.

The first of these is bacteria. To gain an indication of water contamination by faecal material, a bacteria called E. coli is measured.

Giardia and Cryptosporidium are protozoa of increasing concern in drinking-waters, so these are also Priority 1 determinands. Because direct testing for these protozoa is often not practicable, the standards offer options for stopping their passage. Treatment processes such as coagulation and filtration are recognised as effective when properly managed.

The standards specify how frequently monitoring samples must be taken, such as monthly for a small supply through to at least daily for a metropolitan area. In all cases, a minimum of a year’s sampling is required to demonstrate compliance with the standards.

Possible Reasons for E. coli Non-Compliance in the Zone or Plant

Factor Explanation
Transgressions E. coli detected in more water samples than the minimum number allowable for a zone or plant of this population.
No samples taken No E. coli samples taken (or recorded.)
Not enough samples Some monitoring samples taken, but not enough. (The Standards specify how many and how often, etc.)
Inadequate Scheduling Enough samples were taken, but either there were excessively long gaps between samples at some dates, or else samples were concentrated on too few days of the week. (For example, if all samples are taken on Mondays, the supply will not comply.)
No evidence that corrective actions were taken If E. coli transgressions are found in monitoring samples, the water supplier must take appropriate corrective actions to recheck the quality, fix any problems, and if necessary inform health authorities and warn consumers.
Corrective Actions taken, but delayed Corrective actions taken too slowly to meet the requirements of the Standards and to minimise the potential risk to consumers.
Not a recognised laboratory Only samples analysed by a Ministry of Health recognised laboratory are acceptable for demonstrating compliance. Who are these laboratories?

What are Priority 2 determinands?

A second level of potential contaminants, known appropriately as "Priority 2 determinands", is also defined in the standards. These are determinands known to have adverse effects upon human health. Unlike Priority 1 determinands, they do not have to be measured in every supply. Monitoring is usually required if the Ministry of Health believes that levels in a particular supply exceed half the maximum allowable value (MAV) for a particular health-significant determinand.

How is a Priority 2 determinand identified? ESR, a Crown Research Institute, initially assessed supplies on behalf of the Ministry of Health. It used questionnaires and targeted testing to identify those supplies where significant levels of a particular chemical were likely to be present. Through formal procedures, the Ministry of Health then confirmed these chemicals as Priority 2 determinands for that particular supply .In general, only supplies serving at least 500 people were officially assigned these, although fluoridated supplies of any size are assigned one for fluoride.


Currently around 150 Priority 2 determinands have been assigned, with about 50 assigned to treatment plants and 100 to distribution zones (see latest figures). They are included in the listings for these supplies, where they will appear as "Test for:' items like this:

  ZONE:   zonecode        zonename           5,000       De
                   Test for: Arsenic

The water supplier is then required to test regularly for that chemical in the supply, to confirm that it remains below the MAV. Weekly testing is required for fluoride, but for other chemicals it is usually monthly. If concentrations measured remain less than half the MAV for 12 consecutive months, and the assessors are satisfied that the risk is not significant, then that Priority 2 will be removed from the supply's requirements.

In recent years, Drinking Water Assessors have been given the responsibility for assigning and removing Priority 2 determinands.

All Priority 2 determinands listed on this website are chemicals, but micro-organisms or radiological constituents can also be defined.

Why is fluoride a Priority 2?

If you see fluoride beside your supply, it will most likely be because fluoride has been added at the treatment plant to help fight against tooth decay. It is not a contaminant or a health risk at the usual level of application, but since it is potentially a health risk at higher concentrations, it is important that it be regularly monitored. While the Priority 2 general requirement is monthly monitoring, fluoridated supplies must be tested at least weekly.

See all NZ fluoridated supplies

In some areas of the world, fluoride naturally appears at excessive levels in groundwater. However, this is very rare in New Zealand.


An increased emphasis is being placed upon suppliers implementing Water Safety Plans for their supplies, rather than relying upon compliance monitoring as the primary means of detecting problems.


Some Frequently Asked Questions

What is E. coli and why is it measured?

A danger wih any water supply is that human or animal excrement can somehow contaminate the water, passing on illness-causing micro-organisms (pathogens) to those who later drink it.

Analysis of water for all possible pathogens would be prohibitively expensive, so some sort of "indicator' test is required - a test for something that will give an indication of how microbiologically safe the water is for drinking. E. coli is that indicator.

E. coli, or Escherichia coli, to use its full name, is a common gut bacteria living in humans and warm-blooded animals and excreted by them.

While it doesn't usually cause illness on its own (there are some serious exceptions), its presence in drinking-water is used to indicate that the water has been subjected to recent faecal contamination. Therefore if E. coli is present, there is a greater risk of pathogens also being there.

What is FAC?

FAC is 'Free Available Chlorine", and refers to residual chlorine remaining in water after it has been chlorinated. Treatment plant operators can measure the FAC, either on a single sample or continuously using a probe.

This FAC is "Available" to provide a certain amount of disinfection should bacteria be present anywhere in the reticulation. Its continuous presence, above a certain minimum level, indicates that water leaving the treatment plant has been adequately treated for bacteria.

What are Giardia and Cryptosporidium?    Go to top

These are protozoa, single-celled micro-organisms that are somewhat larger than bacteria and have a tough outer coat. They live and multiply in the intestine, causing fever, diarrhea, abdominal cramps and vomiting, which can last for many days. In some people, especially those with weakened immune systems, the illness can be life-threatening.

In water sources they may exist for long periods as cysts, multiplying only after re-entering the intestine of a human or warm-blooded animal.

Unlike E. coli and other bacteria, Cryptosporidium especially are very resistant to chlorination. Therefore treament focuses on very fine filtration to remove them, disinfection with ozone or chlorine dioxide, or the use of deep groundwater that is known to be secure from surface contamination.

Who is responsible for this website?    Go to top

This site is run by the ESR Water Information Systems team, a mix of scientists and information systems people based in Christchurch, New Zealand, and performing science-based drinking water work under contract to the Ministry of Health.

ESR, or the "Institute of Environmental Science and Research Limited", is a Crown Research Institute with major sites in Auckland, Wellington and Christchurch. Contact details here.










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