Contamination of drinking water by stealthy chemicals has set back Auckland's efforts to cope with drought and growing demands on water.
The city boosted its water capacity since the 2020 drought, but it has now lost part of that due to toxic PFAS shutting down its treatment plant at Onehunga, in response to "very low" health risks.
That takes 18 million litres a day out of the system.
An internal Watercare memo says this means it will bring forward its plans to take more water out of the Waikato River under new consents.
"The removal of Onehunga ... will see a significant reduction in our headroom at peak summer demands," a September memo said. Read the document here.
"The impact on annual drought is less pronounced but will result in increased operational costs.
"Another flow-on effect will be the need to lift the drought trigger levels."
Any lift activates drought restrictions sooner.
The lift would be by a tiny amount, about 0.2 percent, when next the levels are reviewed, Watercare told RNZ. It would go the opposite way when the extra Waikato water take was activated, it said.
It was still "in a good position" despite the shutdown, Watercare told RNZ.
PFAS, dubbed 'forever chemicals' for how they persist in nature and can build up in the body, have been causing headaches for water supply authorities in many countries.
Contamination from firefighting foam containing the banned chemicals forced Manawatu to install a new $12m water system at Ohakea this year.
Watercare has spent more than $200m million drought-proofing the system since 2020.
But its reports released under the LGOIMA warn of higher operational and capital costs ahead.
"Earlier utilisation of Waikato" will result in "increased operational cost", the memo said.
Chief operations officer Mark Bourne signed off on the Onehunga shutdown on 17 October, writing:
"Please consider what network improvements (potential capex) are required to improve resilience.
"Based on the timeframe for Onehunga WTP to be OOS [out of service] it may be prudent to undertake this work."
'More production capacity'
However, Watercare said it continued to have more capacity than prior to the 2020 drought, plus Aucklanders were being more water efficient.
"We are confident that the actions we're taking to mitigate the issues removes any risks to the reliability of Auckland's water supply," a spokesperson said.
It had added 12 million litres a day (MLD) capacity at Pukekohe and Waitākere treatment plants; and would soon open a 12 MLD plant at Papakura.
During the 2020 drought, it built a 50+ MLD plant as part of boosting its take from the Waikato River to up to 300MLD, twice what it was prior to this year.
"We are currently seeking confirmation of our ability to utilise the allocation this summer, should we need it," a spokesperson said.
The reports show Watercare got reassuring health advice about PFAS but shut down Onehunga out of an abundance of caution so as not to "erode the trust of customers".
Trace levels of the manmade chemicals showed up back in 2018.
Subsequent monthly testing detected four occasions since 2019 when levels went high - on 8 June this year, water tested at almost twice the new drinking water maximums.
Those maximums kicked in last month, forcing Watercare to decide whether to shut Onehunga.
'Do nothing'
One option was to "do nothing" - "This will result in the treated water from the Onehunga supply being non-compliant from time to time."
"The current issue we face is that we cannot predict the trends at present," a report said.
"Therefore, by the time the sample is taken, the water has already been consumed by customers."
It had an eye on Three Waters.
"Despite the risk to human health from intermittent exceedances ... being very low there is still likely to be concern by customers and the intermittent non-compliances are likely to erode the trust of customers in the safety of the Onehunga water supply and Watercare.
"This is likely to occur at a time of increased focus on Watercare due to the current reforms underway."
Nearly all New Zealanders have PFAS in their blood in trace amounts.
Lengthy high exposure is linked with decreased immune responses, dyslipidemia, decreased birth weight and impacts on liver enzymes. Research is continuing into its impacts on kidney, testicular and breast cancer, pre-eclampsia, thyroid disease and ulcerative colitis.
PFAS polluters have paid out hundreds of millions of dollars to settle lawsuits in the US.
An ESR report to Watercare Read the document here in October concluded the levels "are unlikely to cause immediate adverse health effects" and "are unlikely to have contributed to any major health effects in the population".
There was a higher risk for toddlers, it said.
"As the information on possible dietary exposure to these compounds in New Zealand is uncertain and the (limited) data showing the PFAS burden in New Zealanders is sufficiently high to warrant reduction in exposure, it is recommended that this water contamination is investigated further," ESR said.
There is no easy or cheap fix.
The reports show Watercare first began trying to find ways to treat PFAS back in 2018, but has not got there yet.
Costs arise not just from trying to find a way to get rid of it, but from having to shore up water supply resiliency in the meantime.
Onehunga residents and businesses will now be supplied from the metropolitan water network, with water that is fluoridated.
