Following the Great Drought of 1994, when Aucklanders were left with just five weeks of water supply left in the main Hunua Ranges dams, the big focus has been on future-proofing against a repeat performance.

After a year long inquest, the solution arrived at was a giant faucet connected to the mighty Waikato River.

This, agreed the boffins, would ensure Aucklanders a guaranteed water supply up to a one in 200 year calamity.

Last weekend, just 23 years later, calamity came a-knocking. But it was not the one all the experts advised us to protect against.


Yesterday, while browsing through the documents that gushed forth from the post-1994 inquiry, what stands out is the fixation on drought, as the devil to defeat.

Which was only natural. At a time when the muddy bottoms of the mighty Hunua dams were dangerously close to the surface, and Aucklanders were being told to stick a brick in their toilet cisterns to save water, nobody was warning of Biblical-scale downpours in future times, overfilling the lakes, not just with water, but with debris and filter-clogging silt.

To the Beca Carter consultants, the water from the Hunua Ranges water reserve was the gold standard.

In a wide-ranging investigation into 96 potential additional water sources - towing icebergs from Antarctica at $8 a cubic metre being one - two additional dam sites in the Hunuas scored highest when it came to "raw water quality" and "risk of contamination."

This because "these options are within completely protected catchments and hence have a low risk of contamination."

The reports do acknowledge that global warming was occurring and cautiously mumbled "that annual rainfall in the Auckland area is likely to increase by between 0 and 10 per cent per annum over the next 40 years."

They also noted that climate modelling suggested that the warming of Auckland would be "associated with an increase in the frequency of heavy rainfall."

However, in a report on how to protect against a one in 200 year drought, talk of heavy rain made climate change sound like something to welcome, not worry about.

One lesson of 1994, reinforced again by the weekend's scare in the Hunuas, was the risk of storing our water in too few baskets. Back in 1994, 63 per cent of Auckland's water came from the Hunua Ranges and 31 per cent from Waitakere Ranges.

Today the Waikato River supplies up to 150 million litres a day, so it was a surprise to see Watercare chief executive Raveen Jaduram saying that the Ardmore Water Treatment Plant, which processes the Hunua water, still provides up to two thirds of Auckland's water.

Of course, with Auckland's rapid population growth over the past two decades, it was inevitable that Waikato water was quickly going to graduate from being the back-up emergency source, to a vital addition in the supply chain.

In 2002, when it came on stream, it was sucking 50 million litres a day out of the Waikato.

During the 2013 drought this more than doubled to 125 million litres a day, providing 30 per cent of the region's needs.

Currently, Watercare has a consent to extract 150 million litres a day, and is seeking the right to take an additional 200 million litres in the future.

The reality is, outside the Hunua and Waitakere forest reserves and the Waikato River, Auckland water supply options are limited. Other natural resources are small.

Desalination is expensive and the reprocessing of storm and waste water, though feasible, is unlikely to be palatable to either consumers or politicians.

Mayor Phil Goff, as political leaders tend to do in an emergency, has put on a grave face and demanded an inquiry. Fair enough.

The questions he puts are ones we'd all like answered. In particular, can the Ardmore filter plant be upgraded to better handle another such event?

But let's not spend-up large on outside experts. The latter didn't forewarn, back in the 1994 inquest, of the possibility of last weekend's silt-stirring weather bomb. Why bring them in now to state the obvious.

Despite the scare, water is still flowing and drinkable .... Just. Now it's up to Watercare, to guard against a repeat performance.