This article by Kenneth Davidson cites some disturbing numbers on the extent to which Melbourne Water’s budget has become dominated by paying off of the desalination plant sitting idle 100 km south-east of Melbourne. The arguments that Davidson makes concerning Melbourne’s plentiful supply of water running off the metropolitan area are consistent with our findings, but he doesn’t mention that using that water will bring substantial environmental benefits to our streams and rivers.
The stormwater management system in my inner-city house is also one more small piece of evidence to support his claim that we can easily supply a large proportion of our water from the city’s roofs (and roads). Currently our tank and rain gardens are providing our 4-person house with ~40 L/day of water per person (flushing our toilets, running our washing machine, and keeping our vegetable gardens and shade trees healthy), while we are using well less than 40 L/day per person from the mains supply. This is a system that has been designed with the aim of minimising the frequency and volume of runoff from our property to the street (and therefore to the Yarra River), but a side benefit is the large water savings that it brings to our household.
No one harvesting system is the right fit everywhere, but if we had regulations in place that required retention of stormwater to minimise the impact of each development on its downstream waters, then we would quickly realise that we have a lot more water than we can easily use given the current set up of our drainage and water supply infrastructure. Such regulations could stimulate a market among our water supply authorities: to provide a service to take away all that excess stormwater running off our urban surfaces and making it a substantial augmentation to our water supply system.