Does this look like Melburnians are blatantly ignoring the lesson of the 1997-2009 drought? Average residential water use per person per day in Melbourne (source: Melbourne water system strategy)

The Sunday Age predicted yesterday that Melbourne could begin to run short of water by 2028:

Melbourne could begin to experience chronic water shortages within about a decade, even if the desalination plant is cranked up to its full capacity, as climate change and population growth rapidly deplete the city’s dams.

The paper reckons a key reason is that progress in reducing household water consumption since the millennial drought from 1997 to 2009 has been disappointing:

Average residential water consumption rose to 166 litres a person a day in 2015-16, the highest level seen since the drought ended, figures from Melbourne Water show. It dipped slightly to 162 litres a day in 2016-17.

This sounds awful; it reinforces the campaign The Age has been running recently about how immigration-fuelled population growth is “cramming” Melbourne to breaking point (e.g. see Is immigration ruining our cities?).

But is it that bad? Will Melbourne really “run short of water by 2028”? That’s just a decade away! Well, you can never say never when planning for the future, but it seems unlikely.

What’s going on here is The Sunday Age has chosen to selectively highlight the worst-case scenario from the modelling work done for the Melbourne water system strategy. That scenario is by definition very pessimistic; it assumes the population by 2065 will be “greater than the current Victoria in Future projections” and, moreover, that there’ll be a “42% to 55% reduction in streamflow in rivers across the region”.

Under the other two modelled scenarios – which also account for population growth and climate change – water shortfalls don’t begin to emerge, assuming nothing is done, until circa 2065 or 2043, respectively. The report of the Melbourne water system strategy reaches a less cataclysmic conclusion:

In the longer term, with climate change and population growth, the capacity of the water supply system may need to be augmented within the next 50 years to ensure that enough water is available to meet all of our customers’ needs across Melbourne and the surrounding region…

The Sunday Age’s framing of water consumption as “the highest level seen since the drought ended” is also highly selective. As the exhibit shows, per capita water consumption fell from well over 200 litres during most of the millennium drought to around 160 litres at present. Yes, it’s up a little from circa 150 litres at the end of the drought, but there’s little there to support the paper’s catastrophising.

Ignoring beat-ups, is water supply nevertheless likely to be a hard constraint on the capacity of Melbourne – and cities like it – to grow to (say) double its current population, given the exigencies of climate change? Note here that the issue is metropolitan size, irrespective of whether it gets to a much larger population quickly (e.g. high immigration) or slowly (e.g. low immigration). Here are some matters to consider:

  • Population growth increases densities and thereby reduces the demand per person for water e.g. due to smaller gardens. This is consistent with the established finding that dense cities are more sustainable than suburbs and regional centres
  • Cities adapt; demand for water from households and businesses can be moderated in many ways e.g. by pricing, education, water sensitive design, technology, restrictions. The exhibit shows Melburnians (including government) responded strongly to the millennium drought
  • Supply can be increased; sewage can be treated and recycled for uses that don’t require potable water (in some places recycled water is used for drinking water). It’s possible to come close to creating a closed system where almost all water is recycled
  • There are other potential sources of supply e.g. collection of rainwater/stormwater
  • Victoria’s “water grid” of pipelines means water can potentially be “imported” from regions with spare water
  • Building more dams is off the table, but Melbourne has the option of expanding its existing desalination capacity
  • Much of Australia has worse water security than Melbourne (including many parts of regional Victoria), but there are some places that can provide water at lower cost. They don’t, however, offer the same economic and social advantages of Melbourne’s large population, industry base, and established infrastructure.

A larger Melbourne will need to spend money on augmenting infrastructure. There’s nothing surprising or unusual about the need to increase capacity as demand or variability increases. It’s a commonplace; we’ve done it for centuries and we do it in other areas e.g. Melbourne Metro. What’s important is to minimise the financial and environmental cost by, for example, moderating demand so that costly new infrastructure can be delayed or possibly even avoided.

The cost of supplying water and treating waste in Melbourne needs to be assessed against the cost of accommodating population in other places. There are large economies of scale in this industry. Water supply is in any event only one factor that determines the cost base of a city; it’s significance must be assessed in the context of total costs and benefits.