What’s the Use of Desalinated Water?

Stephen Gray, Director of the Institute for Sustainability and Innovation at Victoria University, recently wrote that Melbourne’s desalination plant would play a vital role in providing water in a drying climate. Max Thomas says we should be careful to not promote a wasteful consumption of desalinated water and instead encourage a sustainable water use culture.

In October 2015, the Premier of Victoria was quoted as suggesting that the water desalination plant constructed near Wonthaggi on the coast south-east of Melbourne could be used to relieve water shortages in Victoria’s north. It now appears that this idea might have originated at Victoria University.

Pumping water up the controversial north-south pipeline would add substantial energy and financial costs to the already expensive desalinated water. At $2,500 per mega litre, it would cost around $25,000 to irrigate 1 hectare of land north of the divide, and that doesn’t include infrastructure and all the other costs associated with efficient water use. Director of the Institute for Sustainability and Innovation at Victoria University, Stephen Gray, says that “farmers are reducing the number of cattle on the land.” But don’t be surprised if there’s not a lot of demand for water to irrigate pasture at $2,500 per mega litre.

Mr Gray goes on to say: “Water from the desalination plant will be delivered to regional Victoria via the state’s rivers and pipe networks.” If the Goulburn River, for example, is to be used as a conduit, the impact on water quality would be such that it would need to be retreated for domestic use. How much of this very expensive water would evaporate or find its way into already depleted aquifers on the way to its point of extraction? Running the desalination plant close to capacity, assuming no breakdowns and with good irrigation efficiency, the daily output would supply enough water to irrigate only a few hundred hectares, leaving nothing for Melbourne. This isn’t really a proposal to be taken seriously, is it?

A high percentage of water is used outside of the house which suggests that major water savings can be made by changing ‘discretionary’ use habits. Stephen Gray writes: “I’m now enjoying my garden, which has sprung to life in recent years, and will be happy if we can avoid such water restrictions again.” This seems very out of step with many citizens who were well ahead of government. They have established drought-tolerant gardens and are still saving water because they want to live according to the capability of the Australian landscape. The botanic gardens at Cranbourne, south-east of Melbourne, demonstrates the concepts and practices very well.

It’s as though there are no ecological ‘opportunity costs’ when water is diverted for human consumption, especially during prolonged drought. In other words, water wasted on gardens could be flowing in streams or put to more beneficial use. Only a very small percentage of water that is treated at great cost is used for purposes where drinking water quality is required. Promoting the use of drinking water for low-grade purposes is anachronistic and wasteful. The arguments for doing so are weak and appear to be aimed at a demographic stratum that would benefit from education to be expected from a reputable university.

“Australia’s rainfall patterns are among the most variable in the world, and prolonged periods of dry weather are normal. However, climate change predictions indicate longer, more severe periods of dry weather. Parts of Victoria have received less than 50% of average annual rainfall for the past two years.” Formulating policy requires a closer analysis than this. Water demand for irrigation depends more on the seasonal distribution of rainfall than the annual aggregate. Subtle shifts in seasonal rainfall distribution could render historically productive land uses uneconomic. Increased summer rainfall might create new opportunities at the expense of existing ones. But increased runoff from intense storms and more evaporation could reduce the amount of plant-available water in soils. Soil erosion might also become more difficult to manage. Predicting these changes with sufficient accuracy to support major decision-making at this stage would be a high-risk strategy.

“Given Melbourne has access to desalinated water that we are only just starting to use, it is unlikely Melbourne will need to consider recycling water for drinking in the near future. However, regional communities may like to have this option, and I believe this option should be allowed.” My guess is that regional communities would be less likely to accept direct recycling of treated sewage for drinking than city dwellers. They will certainly resent being expected to accept water they perceive to be inferior or possibly contaminated. Indirect recycling for drinking is more acceptable because the treated water is released into a catchment area or injected into groundwater where it mixes with naturally occurring water before long periods of storage. However, the process used to treat waste water for drinking requires special skills and the cost of doing it on a small scale would be prohibitive without major financial support from government. At first glance, delivering recycled and drinking water to homes via a single pipe seems a good idea, but why treat all the water supply to drinking standard, at great cost, and then use the bulk of it to water gardens and wash cars and driveways etc? Fortunately, those responsible for making decisions about this are unlikely to be convinced by anything less than sound evidence-based argument.

It would serve no purpose to conjecture about the motives behind promoting wasteful use of desalinated water. The day will probably come when the desalination plant will be seen as prudent drought ‘insurance’ for a rapidly growing city. I hope that will arise from a policy framework designed to promote and encourage a ‘sustainable’ water use culture. Advocating increased use of desalinated water for questionable reasons will ‘throw the baby out with the bathwater’ if it serves only to revive the controversy around the decision to build the plant in the first place.