Traces of a chemical commonly used in plastic packaging have been discovered in an aquifer used to supply Wellington's drinking water.
It's the first time tests for Bisphenol-A or BPA have been made in the Waiwhetu Aquifer, a major source of drinking water for the capital. Water drawn from the aquifer is treated before it reaches households.
Bisphenol-A is a chemical used in some plastics; food can linings, thermal receipt paper, and dental sealants. Opinion is divided globally on its health risks but some studies involving fish, mammals and humans have shown it negatively affects the reproductive system and embryo growth as well.
Although the amounts of BPA discovered have been deemed safe by health authorities, two environmental scientists say they are worried about the unknown, long-term effects of everyday consumption.
Greater Wellington Regional Council says the readings recorded in local water supplies are 70 times lower than the safe limit in the United States.
The Ministry of Health said it had no "current concerns" about the safety of Wellington's drinking water.
However, environmental toxicologist Louis Tremblay said it was "news you [didn't] want to hear". Dr Lokesh Padhye, an expert on emerging contaminants, said it was far from just Wellington's problem but the country's.
A report obtained by the Herald, carried out by the firm Jacobs in Wellington in 2017 found varying levels of BPA throughout the aquifer - a natural underground reservoir beneath the Hutt Valley that is fed by river-water seeping into the ground.
Among the 16 bores Jacobs tested, the highest amount of BPA found was 280 nanograms per litre (ng/L) in a bore in the Hutt City CBD. That amount exceeds levels found in the United States and in parts of Europe.
"It's starting to be a bit of a risk," Tremblay said.
"It is concerning that we have such high levels in the bore water."
The health ministry had no information on the comparative levels of BPA in water supplies in New Zealand. A spokesperson said there was "insufficient data to derive a maximum acceptable level for BPA in drinking water".
A Greater Wellington Regional Council spokesperson said the "widespread presence of BPA in groundwater in the aquifer appears to be consistent with the general occurrence of BPA in groundwater reported elsewhere in the world".
The most Padhye found back in 2011 when he tested for BPA in source water in the southeast United States, was just 22 ng/L. He said even after it went through a treatment plant, there was still 3 ng/L present when it came out of the tap.
The discovery was enough to spark regulations to be brought in and for treatment processes to be strengthened in the state. Shortly after, Minnesota's health authorities also decided on a maximum limit for BPA in drinking water of 20,000 ng/L. That limit is what New Zealand measures its BPA levels in drinking water up against, as it has no such guidelines of its own.
It's important to note that Wellingtonians do not drink directly from the aquifer.
Wellington Water Limited manages the next step, which is UV radiation and chlorine treatment that happens prior to supplying the aquifer water to the region. However, Padhye said a "concerning" amount of BPA would still be making its way to the tap.
He said in the United States, the source water he sampled underwent further disinfection and chlorination treatments - as done in Wellington - but only up to 30 per cent of the emerging contaminants, including BPA, were able to be removed from the final product. Jacobs did not test for levels of BPA at the tap end.
A Greater Wellington Regional Council spokesperson said the "widespread presence of BPA in groundwater in the aquifer" appeared to be consistent with what has been reported elsewhere in the world.
So, how much water should we be drinking?
Tremblay pointed to the latest figures from the European Food Safety Authority.
"[It's] about four micrograms per kilogram daily for a human.
"So you can back calculate how much water you would have to drink to reach that. It would be quite a bit of water to reach that but still it's quite high," he says.
It was not just BPA's presence in drinking water that Tremblay was concerned about, but what else might be in there too. "When we start putting them altogether, then you have a soup of contaminants so over time what are the risks… we don't know."
Padhye said the BPA levels found in Wellington challenge the view held about the country's so-called pristine natural sources of drinking water and how protected they were.
He said the plasticiser could only have got there as a result of a combination of local river water infiltration, sewer exfiltration, and or urban stormwater recharge or runoff.
The fact that BPA even got in, Padhye said, served as a warning for many communities around New Zealand which solely relied on drinking water from aquifers (without any treatment), such as Christchurch and Napier.
Up to 50 per cent of the community drinking water supplies around the country are reliant on groundwater.
A significant number of individual rural households also rely on groundwater for their drinking water supply.