Urban Water Minister Don Harwin, though, is quick to reassure the public that Greater Sydney's water supply "is robust and secure with some of the world’s best water storages". There's enough water for another two years "without a single drop of rain falling", he says. Even so, there are signs of emerging problems amid supply disruptions and rising demand. If not addressed, they could deliver nasty and expensive surprises. "We're sleepwalking," says Ian Wright, a senior lecturer at Western Sydney University who was part of the 2016 triennial audit of the Sydney Water Drinking Catchment. "When you lose 25 per cent of your total water storage in 12 months - wow, that's a really steep fall." Dr Wright and others say the government wound back programs that had encouraged people to conserve water, and delayed recycling projects. If those efforts were stepped up, water storage levels, which are now at about two-thirds, won't fall so fast.

Dam levels continue to slide According to the 2017 Metropolitan Water Plan, when Sydney's storage levels dropped to 75 per cent (in April this year), transfers from the Shoalhaven River's Tallowa dam were supposed to kick in. Those didn't happen, with WaterNSW blaming maintenance issues. Loading Predicting rain events with precision is difficult but the bureau's forecast for the October-December period out this week say there's not much sign of above-average rains returning. Temperatures will continue to be abnormally warm, though, suggesting the record evaporation rate in winter across eastern Australia will be extended.

At the current weekly slide of 0.6 percentage points, Sydney's dams will pass the next trigger point of 60 per cent by early November. At those levels, Sydney's Desalination Plant is supposed to start supplying water. Unfortunately, switching on the plant won't be easy after a severe storm - including a possible tornado - ripped through it in December 2015. "The storm damage to the asset was widespread around our 45-hectare site," a spokeswoman for the plant said. "In fact our insurers likened the damage to what is typically expected following an earthquake." The damage done to the Sydney Desalination Plant from a violent storm in December 2015 was likened by its owners to "an earthquake". Credit:Nic Walker A complex operation

Reconstruction of the plant took almost 18 months and testing is now underway ahead of a December 13 restart target. Reaching full production of 250 million litres a day will take at least half a year. Even without the storm damage, recommissioning such plants is complex. The facility - leased in 2012 to three investment funds for $2.3 billion - contains 36,000 polymer membranes that are used to remove salt and other impurities from the seawater. Sitting idle for six years, the membranes have to be checked for bacteria and other fouling, and any required replacements will take time to source. An employee of the Sydney Desalination plant walks past some of its 36,000 polymer membranes used to filter salt and other impurities from seawater so that it can suitable for drinking.

Specialist and trained staff also need to be recruited once the storage trigger is passed - assuming it is. The 18-kilometre pipeline linking the plant to Sydney's main water supply at Erskineville also has to be disinfected, among other steps. "[Those] activities combined involve significant time to achieve from a water security state of preservation, hence the allowance of eight months to complete a restart," the spokeswoman said. Water restrictions? Even with the full ramp-up, the next trigger point could well be crossed: the imposition of Stage 1 water restrictions when storages hit half full. These include requiring trigger nozzles on hoses, and avoidance of watering gardens during the height of the day. Potentially embarrassing for the government, such requirements could happen before the March 23 state elections next year.

Stuart Khan, a professor at the University of NSW's Civil and Environmental Engineering, notes Melbourne's larger desalination plant took almost a full year to deliver water after being ordered to restart by the Victorian government. It had only been shut for four years and hadn't been battered by the elements. "This whole desalination thing is a real worry for [the NSW government]," Professor Khan said. "They don’t want to go into an election with water restrictions being imposed.” Loading Residential customers, now paying on average $94 a year to cover the fixed costs of the desalination plant, won't be amused to cop curbs on water use too. “You will have spent $2 billion building a desalination plant but - due to the government’s inability to make sure thing was ready to be used when they needed it - now the community’s paying for it with water restrictions," Khan said. "I’m sure that’s a risk they are actively trying to avoid.”

Minister Harwin said Sydneysiders had shown they're willing to conserve water without the need for restrictions. "Restrictions can have financial and employment impacts on the community and it would be irresponsible to rush to water restrictions as some have suggested," he said. Chris Minns, Labor's water spokesman, said Harwin’s "low-profile approach to water management has proven to be a disaster with the private operators of the desal plant ignoring him and the Treasurer stealing dividends from under his nose". Sydney Water has funnelled about $2.3 billion to state coffers in the past five years. "His repeated assurances that critical infrastructure would be unlikely to be needed have proven to be false," Minns says. "Ultimately water restrictions are likely to be introduced earlier than necessary due to this government’s negligence." Water security 'taken for granted'

Justin Field, the Greens water spokesman, said there was a case for early imposition of water restrictions, noting per capita water use has been rising since the Liberal-National government took over in 2011. “The government has taken water security for granted due to a false sense of security provided by the desalination plant and an underestimation of the perfect storm of drought and climate change," Field said. Also pushing up water use is Sydney's rising population, increasing at the pace of about 1 million people every 10 years. That pace is expected to continue for decades. Through winter, daily water demand for Greater Sydney - which takes in the Illawarra and Blue Mountains - was 1.514 billion litres, up 4 per cent from the year earlier. Usage was up almost 15 per cent compared with the 10-year rolling average for the season, Sydney Water said. A Sydney Water spokesman said the utility in 2017-18 supplied almost 43 billion litres as part of its recycling efforts. Half of that helped irrigate parks and agriculture.

But, as Khan notes, the 2006 Metropolitan Water Plan had set an annual recycling goal of 70 billion litres of wastewater - by 2015. Sydney Water's 2010 plan identified Hoxton Park as one project that would be up and running by 2015. Instead, it is now expected to be ready only by 2020-21. Khan says there may be reasons for abandoning some of the recycling projects. At some point, though, the government had to develop a serious plan to promote conservation and ways to reuse water. “You panic before you get to zero [storage capacity], surely," he says. "You don’t wait til you’re sucking mud until we all start to get concerned and wondering what we’re going to do next.” Other missed opportunities include ditching the "Every Drop" and other water-savings programs, Khan says.

A 2016 decision by the Independent Pricing and Regulatory Tribunal to set water prices uneconomically low for recycling schemes in new developments such as Barangaroo and Central Park stymied progress on that front. Harwin announced a review of the IPART decision in June last year. The Herald understands IntrastructureNSW completed the report and the Planning Department, which commissioned it, is still considering its results. Field said a "drive for profits" by Sydney Water rather than water efficiency "will cost consumers more and undermine water security". Wright and Khan also highlight other savings that may prove unwise if extreme weather events throw up other unexpected challenges. They say the scientific team at what was the Sydney Catchment Authority had all but been dismantled when it was absorbed into WaterNSW after 2015. The authority - and the scientific team - had been set up following an outbreak of cryptosporidium and giardia in water supplies in 1998 that had Sydneysiders boiling water to avoid infection.