Drinking water quality report – Expert Q&A

The latest annual Ministry of Health report on the quality of New Zealand’s drinking water has revealed 19 per cent of people are exposed to water that doesn’t meet all safety standards.

Some coverage of the report has included calls from Water NZ for all water to be chlorinated or otherwise treated.

Health Minister David Clark today announced changes to the Health Act to improve the existing drinking water safety regime and speed up the process of major reforms to come.

The Science Media Centre asked for comments from experts, including those who prepared the report for the Ministry of Health (see declarations of interest below). Feel free to use these comments in your reporting.


Professor Michael Baker, Professor of Public Health, University of Otago, comments:

Do you think these statistics indicate our water safety standards are at acceptable levels?

“Firstly, this report shows that the water quality monitoring only covers about 80% of the NZ population, being those with registered networked drinking water supplies that serve populations of more than 100 people. The remaining 20% of people are exposed to often unmonitored drinking water supplies for places such as small settlements, schools, and camping grounds. These small drinking water supplies will almost certainly be of lower quality than those covered by this monitoring report. I think this situation is unacceptable and should be addressed.

“Secondly, these data show that almost 20% of monitored supplies do not reach specified standards. This gap means that some communities are exposed to an increased risk of infection, particularly from protozoa such as cryptosporidiosis and giardia. Whether this risk is acceptable depends on the judgement of those affected and the agencies involved in protecting their health. For example, some local communities might decide that they would prefer resources to be invested in making roads safer than in improving drinking water treatment. Obviously, making such decision requires good information. This report would benefit from having more interpretation and analysis to explain the level of risk that communities face if their water supply doesn’t meet protozoan standards.”

Why is the bacteriological standard the most important?

“Water supplies that meet the bacteriological standards provide a reasonable degree of protection against serious bacteria such as campylobacter, which caused the Havelock North outbreak, and verotoxigenic Escherichia coli (VTEC) which can cause very serious illness, particularly in children. Effective treatment of drinking water is arguably the most important public health intervention in recent history as it largely eliminated serious bacterial diseases like typhoid and cholera which had devastated towns and cities in the Victorian period.”

Does independent public health research reinforce the need for tougher standards on drinking water safety?

“The standards themselves appear reasonable. The main problem, highlighted in this report, is that such standards are not being adhered to.”

Do you have concerns about lobby groups weighing in on this debate, when their members stand to benefit from chlorination?

“Lobby groups comment on many public issues. I think it is reasonable for them to do so provided they make it clear where they have a real or potential conflict of interest.”

General comment:

“This report is a useful summary of a range of New Zealand drinking water quality measures. In general the findings show a fairly similar pattern to other recent monitoring reports.

“The good news is that most of the monitored supplies meet bacteriological standards. This means that they provide a reasonable degree of protection.

“The not so good news is that only 83.1% of supplies have measures in place to provide reasonable protection against protozoan pathogens, such as giardia and cryptosporidia.  These pathogens, particularly cryptosporidia, are a widespread contaminant of our rural environment as a result of intensified dairy farming.

“These problems with the safety of drinking water in New Zealand mirror wider concerns about the capacity of our public health sector. Many of us are hoping that the current inquiries into drinking water and the health system more generally will result in a much needed upgrade of our essential public health services and institutions.”

Conflict of interest statement: I have received research funding from the Health Resarch Council to investigate the health effects of the Havelock North campylobacteriosis outbreak.


Dr Chris Nokes , Science Leader, Risk & Response and Social Systems Group, ESR, comments:

Do you think these statistics indicate our water safety standards are at acceptable levels?

“Not meeting the requirements of the Standards does not necessarily indicate that the water is unsafe. Meeting the bacteriological standards has two components: one concerning the quality of the water and one related to whether the sampling programme met requirements such as sampling frequency and period between sampling. The detection of an indicator organism in the water (e.g. E.coli) shows that the water has been in contact with faecal matter. While, it does not show that there are pathogens in the water, there is that possibility and the water supplier needs to respond accordingly.

“That said, there are, no doubt, some water supplies that are at an unacceptable risk of unsafe water. These may well be under-resourced systems”

Why is the bacteriological standard the most important?

“The cases of waterborne outbreaks of disease in New Zealand associated with drinking water that are recorded in Table 1.3 of the document, Guidelines for Drinking-water Quality Management for New Zealand show the majority of these outbreaks are caused by bacteria.

“Water that meets the bacteriological requirements of the Standards is also likely to be safe from most viruses as treatment processes capable of ensuring water is safe from bacterial pathogens are also likely to ensure the water is safe from most viral pathogens.

“Bacteria can cause illness relatively soon after a person has consumed contaminated water. The consequences of infection can be severe and in some circumstances fatal.”

Does independent public health research reinforce the need for tougher standards on drinking water safety?

“There is evidence to show that ensuring drinking water is free of disease-causing organisms is an important measure in protecting public health. The risk management of water supplies should ensure this, and drinking water standards should provide a way of assessing whether this has been achieved.”

Do you have concerns about lobby groups weighing in on this debate, when their members stand to benefit from chlorination?

“I am not greatly concerned by lobby groups becoming involved in the debate provided their arguments are scientifically based and that they do not misrepresent the facts. Presumably, any benefit they might gain from chlorinating a water supply, would be accompanied by a benefit to those receiving safer water.”

Conflict of interest statement:  I am an advisor to the Ministry of Health; ESR prepared the Annual Report for the Ministry of Health.