Water, water, everywhere, nor any drop to drink.
Rime of the Ancient Mariner. Samuel Taylor Coleridge

Within the space of a decade, Australia will have created almost 500 billion litres (GL) of new annual urban water supply, thanks to the ‘miracle’ of seawater desalination. By 2013, all coastal capital cities, with the exception of Darwin and Hobart, will have a major desalination plant.

Nationally, this new water supply capacity will provide about a quarter of all urban water needs. Some cities are rapidly becoming even more reliant on desalination than this figure suggests. When the Port Stanvac desalination plant in Adelaide is completed in late 2012, it will supply 70% of Adelaide’s drinking water (WSAA, 2009).

I used the term ‘miracle’ somewhat ironically in my opening, but it is indeed remarkable how we have moved, in only a few years, from desalination being no more than a specialist water treatment option for remote desert locations, to it being a critical part of mainstream urban water supply security.

The reason for this is well summed up in the recent WSAA Report Card, which states ‘the great virtue of desalination is that it is a reliable source of water, has a small (physical) footprint, and can be constructed in a relatively short period of time’.

And for a politician on a three year election cycle, it is nice to be able to launch the project, and cut the ribbon at the opening ceremony, all within a single term! No dam can ever offer such a rapid water-security outcome for a Premier or Minister.

For urban water suppliers on the Australian coastline, it is the ‘climate independence’ of seawater desalination that is its great attraction. The traditional approach of building new dams to meet increasing water supply requirements holds little water, quite literally, in a drying climate. No point building a new dam if there is no rainfall to fill it.

Demand management can help, but it is unlikely ever to be enough to offset the need for an increasing volume of secure climate-independent supply.

Of course, desalination is not without its downsides and detractors. The biggest concern is the high energy requirement to fuel it, and the potential high greenhouse-gas emissions as a consequence.

Typical energy consumption for seawater desalination is in the range of 4–5 kWh/kL. When the Kwinana desalination plant in Western Australia came on-line in late 2006, annual energy consumption for Perth’s water supply increased from 2000 GJ/GL to 3540 GJ/GL, even though that plant represented less than 20% of water supply (Kenway et al. 2008). In their report, Kenway et al. suggest that, by 2030, in the ‘extreme’ case where desalination meets all the water growth requirements for Australia’s capital cities, energy consumption by capital water supply providers could increase by up to 400%.

To meet this high energy demand, all major urban desalination plants in operation or under construction in Australia have, according to WSAA, significant, or full, green-energy feed-ins. Whether this is enough to allay community concerns about desalination’s greenhouse-gas effects remains to be seen.

There are also concerns about environmental impacts of desalination on coastal waters, and aesthetic issues about unsightly infrastructure adjacent to beaches. The potential marine effects relate to discharge of concentrated brine, and to marine life being accidentally sucked into the plant’s intake. Few scientific data on the extent of the latter problem seem to exist; and detailed modelling studies for positioning outlet pipes and ensuring rapid mixing indicate minimal local changes from discharged brine. Nevertheless, it is very early days, and monitoring programs need to be alert for any impacts.

In 2060, 50 years from now, Australia’s population will have doubled, and the vast majority of those new Aussies will live in coastal towns and cities. Another 20 million people need about 2000 GL more drinking water annually; perhaps 1500 GL if we can get on top of urban water demand management.

Prior to desalination, that would probably have meant at least one new major dam for every coastal capital city. This is one of the environmental upsides of desalination plants.

That is, that no — or fewer — new dams, with their associated negative effects on river ecology, may need to be built for coastal cities.

And by providing a ‘new’ water alternative for these cities, desalination plants could remove the need to transfer irrigation water supplies from inland rural to coastal urban areas, with its associated controversies.

While the urban water industry will continue to invest in other new water sources — stormwater and wastewater recycling most notably — the projected growth in desalination far outstrips projects for water recycling. Over the next decade, in which desalination water supply capacity will reach 500 GL, recycled water supply will increase by only around 100 GL (based on the rate of recycling growth over the past decade).

The desalination die seems irrevocably cast for the Australian urban water supply industry.

Recycling will always be an important component of urban water supply and management, if only for its beneficial environmental outcomes on water quality. But desalination must be seductively attractive to any urban water supply authority in coastal Australia, and is likely to become the major source for meeting future urban water needs.

Are there any downsides to desalination that have not been contemplated? An impossible question to answer, but one that people should, and no doubt will, keep a close eye on over the coming years and decades.

I should make it clear that I am not an opponent of desalination. The ‘seduction’ of desalination I alluded to above is founded on a reasonably compelling case of water security benefits, especially in Australia with our highly coastal population and an increasingly dry climate. I am merely an interested and curious observer of a phenomenon that has emerged so rapidly as to amaze me.

My hesitation, if any, is simply because in moving so fast we may have missed something important. What this might be, I do not know. But I do believe we will need to keep a close eye on desalination over the coming decades to make sure no unintended and unpredicted side-effects pop up to bite us.

If Coleridge’s ancient mariner had a portable desalination plant handy, he would have had little to bemoan. Today in Australia, there seems no stopping the desalination juggernaut.