The ACT's $141 million Murrumbidgee pipeline was forced to shut off a month after it was fired up for the first time because of low levels of water in the river.
The 12-kilometre pipeline was commissioned in 2007 at the height of the millenium drought, amid water restrictions and concerns about Canberra's ongoing water security.
Construction began in 2011 and was completed in September 2012, but with the exception of routine testing every three months, the pipeline has remained dormant.
That changed in July, Icon Water officials told an annual reports hearing on Monday.
“We did operate for a number of weeks, two or three months ago,” business services general manager Jane Breaden said.
“We actually had to stop pumping because there wasn’t sufficient water in the Murrumbidgee for us to continue safely. Again we need to allow for environmental flows also. At the moment the pipeline is in suspension mode.”
Ms Breaden confirmed it was the first time the pipeline had been used specifically for topping up the ACT's water storage levels, which are at their lowest point in five years at 65.43 per cent.
An Icon Water spokeswoman said the pipeline had remained on standby since its commissioning due to a "stronger than anticipated water security position".
Its commissioning coincided with the massive enlargement of Cotter Dam, which increased the territory's overall water storage capacity by 35 per cent.
However total water levels have been steadily falling since a peak of 100 per cent in late 2016.
The pipeline is supposed to kick in when total storage drops below 62 per cent.
It can also be switched from standby to operating mode "as many times as required to keep Googong over 80 per cent".
Googong has been below 80 per cent capacity - and dwindling - since last October.
The Icon Water spokeswoman said when the pump was switched on, Googong was at 72 per cent.
However the exercise served a dual purpose, allowing the pipeline's pumps to be operated for maintenance and engineering purposes.
A report published in August showed all but two maintenance runs had to be postponed in the past year because of low water levels.
After a month of "intermittent" pumping, and a transfer of 430 megalitres, the pump was shut down to protect the minimum daily flow in the Murrumbidgee River.
When pumping began, the Murrumbidgee was flowing at 104 megalitres per day. When the pipeline was shut off, the daily flow was 165 megalitres per day.
While the baseflow was lower when pumping began than when it finished, there are different rules each month for what the minimum base flow can be.
In July, the minimum base flow is 89.3 megalitres per day while in August, the minimum flow is 133.6 megalitres per day.
Icon Water’s chief executive Ray Hezkial said these rules meant there was a "careful balance of environmental values and the community’s water security needs".
"[The Murrumbidgee to Googong pipeline] is a valuable water supply option which is the best available way in which to supplement Googong Dam for the community’s water supply. The [pipeline] has allowed diversification of water supply options so that we can balance supplies and operating costs,” Mr Hezkial said.
The company said in September water restrictions were unlikely to be needed for 20 years based on climate modelling, current storage and consumption levels, despite farmers on land surrounding the capital struggling through drought.
However an ACT government spokesman said water restrictions could be brought in sooner if dry conditions persisted.
Conservation Council ACT executive director Larry O'Loughlin said the territory also needed water policies that encouraged water re-use, minimised raw water consumption, conserved water from roofs and built wetlands and stormwater ponds.
"While we need to have access to secure water supplies, we should minimise our raw water use so that we are not a drain on the region around us. We need to first reduce water consumption and apply water conservation before we take water from other sources such as the Murrumbidgee," Mr O'Loughlin said.
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