About Water

written by Peter Croft

Where do you start when you look into the topic of water? There are so many aspects.

International
At an international level, at least 10% of the world’s population (around 700 million) do not have access to clean water each day.

A growing world population – from 7 billion now to 9 billion by 2050 – and the associated need for more food will stress existing supplies of fresh water.

The actions of upstream nations on draw-downs of river water already affect downstream nations: the Mekong and Niger rivers are examples. Some of these actions might lead to future conflict between nations as a result.

Then there’s climate change and its likely effects on future water supplies, amongst many more water issues.

Australia
Let’s narrow the focus down to Australia. The Frank Fenner Foundation has a short summary of water issues that is worth reading (at http://www.natsoc.org.au/our-projects/biosensitivefutures/part-4-facts-and-principles/ecological-issues/water-issues-in-australia). The summary paints the picture of land-clearing for agricultural purposes and the regulation and diversion of rivers to support agriculture. Some quotes from this summary:
“Rivers have also been dammed for domestic and industrial supply, but this component comprises a very small part of the big picture. By far the largest demand on Australia’s water resources – 75% of all surface water use – comes from irrigated agriculture.”

“The amount of water used in agricultural production means that our food choices can have much more impact on the water cycle than our domestic water use. It remains a surprisingly poorly researched area, but work that has been conducted in this field has demonstrated that the ‘embodied’ water in our daily purchases can far outweigh the direct water use in our households.

For example, studies have estimated that approximately 700L of water are embodied in a typical one-litre carton of milk, attributable to the water requirements to grow pasture for dairy cattle. This is greater than the amount of water required to wash 10 loads of laundry in a front-loading washing machine!”

The Murray-Darling Basin
Narrowing the focus of this topic even further, let’s consider the Murray-Darling Basin and the experiences of the Millennium drought (finishing in 2010), particularly in South Australia. Telling the story involves describing the number of gigalitres (billions of litres of water) that are involved.

In 2007-08, CSIRO, as part of its Sustainable Yields Study, modeled several future climate scenarios for the Murray-Darling Basin catchment and the impacts on the water available for environmental, agricultural and domestic/industrial purposes.

The Executive Summary of the Sustainable Yields study states that under the “Recent Climate and Current Development” scenario (a likely future scenario), “The end-of-system flow of the Murray River has been significantly reduced by water resource development. The average annual end-of-system flow under without-development conditions (but including Snowy Mountains Hydro-electric Scheme contributions) is 12,233 GL/year and this has been reduced by 61 percent to 4733 GL/year on average as a result of water resource development.”

CSIRO also reported that, in this scenario, “Cease-to-flow conditions occur at the Murray River mouth 1 percent of the time under without-development conditions; under current development conditions flow ceases 40 percent of the time”.

The significance of Cease-to-flow (i.e. the Murray Mouth is effectively closed) is that the Murray is unable to discharge its salt load out to sea. Each year, the River Murray carries an average of two million tonnes of salt to the Murray Mouth and out to sea (that’s about four tonnes per minute!). The Murray Mouth is the only point where this salt leaves the Murray-Darling Basin. This salt is drawn from all of the upstream landscapes in New South Wales, Victoria and South Australia. When the Murray Mouth is closed, all of that salt ends up in the Lower Lakes – Lake Alexandrina and Lake Albert. In the Millennium drought, that is exactly what happened: salinity levels in both lakes rose markedly, (in Lake Albert – to almost 1/3 the salinity of seawater), and the lakes could no longer be used for drinking purposes by stock, crops or humans.

In 2009, so little water was entering the Lower Lakes that the evaporation from the Lakes far exceeded the inflows down the Murray (at one point only about one gigalitre per day of inflows!). Yet evaporation amounts to almost 3 gigalitres per day on average, and much more in summer. As the lake level dropped and the edges of the lakes became exposed, the iron sediments in the soils generated vast volumes of sulphuric acid and the lakes came very close to complete collapse.

Greater Adelaide
As the salinity in the Lakes increases, so the probability of salt slugs making their way back up the river increases. And, if those salt slugs reach the intakes at the pumping stations that provide water for Greater Adelaide, there are major risks to the city and South Australia’s country towns.

Could water restrictions in Adelaide have made up the difference? In short, no: Greater Adelaide uses around 200 gigalitres of water per year. (refer water-for-good-summary-plan-2.pdf). With Level 3 water restrictions, this drops to around 170 gigalitres. Our dams, if full, hold about one year’s water supply. In the Millennium drought, dam holdings were much lower and South Australia was very dependent on River Murray water. The situation was sufficiently dire (there was no end in sight for the drought) that a desalination plant was commissioned to produce 100 gigalitres of water per annum as an “insurance” policy. If Greater Adelaide had moved to level 5 restrictions, (basically no watering outside the house), only about 30 gigalitres per annum would have been saved but much vegetation and gardens would have been lost. Those 30 gigalitres represented not much more than a week’s evaporation of the Lower Lakes.

With the end of that drought, attention was focussed on creating the Murray-Darling Basin Plan to ensure that the Basin was run on a much more sustainable basis. Under this Plan, over 3000 gigalitres per annum of water is intended to be purchased or released through efficiency gains to ensure that there is sufficient water in the Lower Lakes to keep the Murray Mouth open and flush out the Basin’s salt to the sea. Should this water not be accumulated, the next drought will again put Adelaide and South Australia at great risk.

What can we do?
The story above highlights that there is indeed a “bigger picture”. Agriculture uses most of the water in the Murray-Darling Basin and water restrictions in Greater Adelaide make a useful but quite modest contribution to ensuring that the Basin is healthy. Nonetheless, a useful goal for any individual or community is to reduce their water usage as it increases resilience in the face of the expected upturn in drought years in the future. There will be no point in having a lifestyle or garden that requires lots of water to maintain when (not if) restrictions are next applied.