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  • Writer's pictureGary Moller

Is bathing in Central North Island thermal water endangering your health?

(updated April 2022)


Arsenic is the most common toxin seen in hair tissue analysis in New Zealand. Treated timber and geothermal water are the two most common sources of arsenic, with the third being contaminated bore water. These appear to be taboo topics for discussion, probably due to thermal pool tourism, and our reliance on softwoods as building materials. Some regions such as Central Otago rely on bore water. If arsenic is in the rock strata this may contaminate the water supply.

Softwoods usually require treatment with chemicals, including arsenic to prevent rotting and infestation by insects. Unlike manual saws, chisels and planes, modern high-powered woodworking machinery creates fine dust and the heat vaporises chemicals, including arsenic. So, despite modern health and safety practices, the problem is getting worse rather than better.

Bathing in geothermal waters is a popular past-time with many health claims. Some waters, particularly the central North Island have extremely high levels of arsenic.

Working with arsenic-treated timber or bathing in some geothermal pools exposes the person to the risk of arsenic contamination: This is a fact!

The questions to be answered are these:

  1. How many people in New Zealand have toxic levels of arsenic in their bodies?

  2. What are the consequences to their health?

  3. Assuming there is a public health problem here; what, if anything, is being done about it?

The evidence leads me to conclude that countless thousands of people have had their health compromised by exposure to arsenic. I have now had so many cases of arsenic-related ill health that it runs into the hundreds, perhaps more than one thousand: I have lost count.

This article is about the hazards of bating in geothermal water which contains toxic levels of arsenic.


Is bathing in Central North Island thermal water endangering your health?

In a word, the answer is "Yes!", if you bathe in the wrong waters. There are thermal pools in the Central North Island that are so toxic with arsenic that they should be shut down, or at least, come with health risk warnings. The highest levels of arsenic-contaminated thermal waters tend to concentrate in the Tokaanu region, bordering Lake Taupo. This may represent a hazard to health.

I asked this question myself, when my partner, Alofa fell unusually ill after bathing in private mineral pools in Tokaanu. It gradually dawned on us that she had been affected by a poison, which was later identified as arsenic. While she was successfully treated, the process of learning more about the source of contamination, then confirming it with laboratory tests of the suspect water and identifying other cases of ill health coinciding with bathing in the same water has taken a while. I am now confident of the evidence to put it out for public attention and scrutiny. Hence this report.

How arsenic gets into geothermal water

I am not an expert in geothermal geology; but here is my understanding of what is going on:

High levels of arsenic in thermal water happen when super-heated subterranean geothermal water passes through arsenic-laced rock while on its way to the surface, dissolving the mineral as it goes. One geothermal spring may be high in arsenic and/or other minerals; whereas another adjacent to it may have a different composition: it all depends on what kind of rock the water passes through.

Some, if not all geothermal springs in Tokaanu, pass through arsenic-laced rock, producing some extremely high readings of arsenic in the water.