CuriousCity: How Wellington's drinking water is kept free of contamination
Chlorinated, fluoridated, then delivered to your glass. Rachel Thomas finds out how Wellington's drinking water is looked after.
It is pertinent that the day Stuff decides to learn more about Wellington's water, it is forcing itself down upon us in frozen chunks of hail.
We are at Te Marua Water Treatment Plant in Upper Hutt, also known as Kaitoke, which serves as the main freshwater treatment plant for 400,000 residents across the Wellington region.
Kaitoke and Wainuiomata are home to Wellington's two river-based water sources.
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Greater Wellington Regional Council chairman Chris Laidlaw says the catchments of both the river sources in Kaitoke and Wainuiomata are in protected forest parks where there is virtually no human activity.
"There's no agriculture up there and very little intrusions with the water. It's pure water we get from the hills."
That said, all water sourced from rivers is at permanent risk of contamination from faecal or other organic matter.
That is why it is chlorinated, says Lower Hutt Deputy Mayor David Bassett, who is also chairman of Wellington Water's governance committee.
"It's better to err on the side of caution, and we are very risk averse when it comes to Wellington's river water supply."
Most of the residents in Lower Hutt, Upper Hutt, Porirua and Wellington get either chlorinated river water, or a mix of chlorinated river water and aquifer water.
The region's confined aquifer can be found at Waiwhetu in Lower Hutt. It is the only source of unchlorinated, unfluoridated water in the region, and supplies drinking water to more than 70,000 Hutt City residents.
Water from the aquifer is free of bacteria and other contaminants, Bassett says.
That is because it is at least a year old and goes through a natural filtration process as it makes its way through the aquifer layers.
"It doesn't need to be chlorinated, and so long as the network [of pipes] is secure, it is safe to drink at the tap – and we test the water throughout the network to make sure that it remains safe."
Over the past year, there have been four positive E.coli tests at reservoirs in the unchlorinated network, Bassett says.
When that happens, Wellington Water notifies regional health authorities, shuts off the system, chlorinates the relevant reservoir, and re-tests the water until it is all-clear.
There were no reported instances of illness relating to any of these cases, he says.
Before the Havelock North campylobacter outbreak, Wellington Water tested for E.Coli three to four times a week at the bores fed by the Waiwhetu aquifer.
Since the outbreak, daily testing has been done at the individual bores.
"This ensures we know exactly how each bore is performing."
As well as testing, there is training, safety measures and operational procedures that keep the water in the network safe to drink all the way to the tap.
It is an intense programme, but for good reason, Bassett says.
"We know safe and reliable drinking water is vital to the health and prosperity of our region and its people".