Of course they are running the line that the 50 gigalitres that the government have ordered from our desalination plant next summer is drawing on our insurance policy (that is costing us something like $600 million dollars a year before they turn it on, and substantially more for the water delivered, while it adds a significant draw on the state’s energy supply).
And what has precipitated this decision? The drop of our water storages to below 64% full.
Meanwhile at our house, our vegetable raingardens continue to drink happily from their stored stormwater, with no need for topping up by mains water at all. Sure, we are now entering a hot week that is the 5th week without significant rain, but our tank only finally emptied last night, which means that we might use 600 or 700 litres extra of mains water before it rains next*. But, over the last year we have used 40,000 litres of our roof runoff.
Our house is much smaller than average, meaning that the average house in Melbourne could easily harvest more than we do, but let’s for the sake of argument say that half a million of Melbourne’s houses and office buildings had similar systems installed that saved the same amount of water each year. Those half a million houses around Melbourne would have drawn 40,000 litres x 500,000 systems = 20 gigalitres less from our dams each year (surely a very conservative estimate).
If we had have worked to install half a million similar systems over the last ten years instead of building the desal plant, our dams would be substantially fuller now, and we wouldn’t be talking about a need to augment their supply. The cost to the community of such a hare-brained scheme? Assuming costs of $10,000 per property (~20% more than our cost, some of which we were able to absorb because it was part of a larger renovation), systems like ours on half a million houses would have cost $5 billion dollars: about a quarter of the desal plant’s total costs: i.e. the minimum cost assuming it delivers no water).
And of course that’s not even thinking about the other benefits of urban cooling, flood protection, river protection and reduced energy consumption, that such a scheme would provide that we are missing out on by investing in the desalination plant.
*As it happens we received 3.2 mm of unexpected rain that night, so we are back using tank water 2 days after it emptied.