The water-saving effort in Melbourne has been admired in many parts of the world as a great example of a successful behaviour-change campaign.
As I drove past a park with a sprinkler on in the heat of the day last week, I wondered whether we are forgetting the lessons of the millennium drought. It's not a bad thing to be irrigating parks in summer to provide cool, green places, but using the sprinkler when evaporation is at its highest makes little sense.
Melburnians were world's best water-savers between 2000 and 2010. Indeed, water use per person reduced by more than 40 per cent compared to the decade before. Without this water-saving effort, Melbourne's drinking supplies would have run dry around June 2009.
Back in 2009-10, Melbourne's households were using 146 litres of water per person per day. During the summer of that year household daily use was kept to 158 litres per person, close to the target of 155 litres.
But last month Melbourne's daily household water use peaked at 255 litres a person. This follows a steady increase over the past few years. Last summer we used 211 litres per person per day, and we are on track to use at least that amount this summer.
Of course, with the extra rainfall of the past few years and the lifting of water restrictions, some increase in water use is to be expected. Higher summer temperatures this year would also be expected to drive increased water use and we need to water our parks and gardens. However, even accounting for these factors, it doesn't make sense to go back to our old water-wasting habits.
The water-saving effort in Melbourne has been admired in many parts of the world as a great example of a successful behaviour-change campaign. When the Bracks government started the campaign in 2002, the target was a 12 per cent reduction in water use per head by 2010. This target was far exceeded and by 2006, even without water restrictions, Melburnians were saving 22 per cent compared with the previous decade.
The campaign was backed by rebates on water-saving products, water restrictions and permanent water-saving rules, tiered pricing to reward water-saving, rules requiring major industry to carry out water audits, and a public social marketing campaign.
Newspapers prominently published the level of water in our dams, and water authorities informed people how much water they were using compared to their neighbours. The information increased water literacy, but the campaign also garnered something even more important: an emotional commitment to the water-saving effort from the whole family. How many parents had their children criticising them for letting the water run while they brushed their teeth or washed the potatoes?
The massive reduction during the millennium drought in stream flow that fed Melbourne's water supplies raised the risk that Melbourne would not have enough water to supply its growing population even with the water conservation effort. This would be unthinkable and led to the decision to build the desalination plant at Wonthaggi. While this has been controversial in some quarters, particularly after it started raining in 2010, I've no doubt it will be needed.
Melbourne's population continues to grow quickly and is likely to be 5 million in just over a decade. We haven't had an El Nino for some years, but when we do rainfall is likely to reduce considerably.
We now know that stream flow into our dams is likely to reduce even more than rainfall. This is because hotter, drier conditions mean the land surface is not as moist when rains come, and there is less runoff into the dams. The higher temperatures we expect from climate change will also contribute to increased evaporation, thereby intensifying the impact of rainfall reduction on stream flows. Scientists have now found that global warming appears to be changing pressures along the subtropical ridge over Australia, which in turn is leading to declining rainfall over Victoria.
As the Napthine government's recently released water strategy says, under a ''business as usual'' scenario it may be necessary to commit to two additional desalination plants, at a total cost of $6 billion, during the planning period to 2050. The strategy therefore recommends that we instead make use of local stormwater harvesting (wetlands, lakes, rain gardens and tanks) and recycled water to boost our supplies. This makes sense, but it will be some time before these alternative forms of local supply will build to a substantial contribution, so we need to start implementing them now.
While we do this, it is vital that we do not take our eye off the water conservation ball. Water conservation has been contributing more than 200 billion litres of water a year to our supplies - more even than the total capacity of the desalination plant. It is too good to waste.
John Thwaites was a minister for water in the former Labor state government and is chairman of the Monash Sustainability Institute.