Land use is an important factor when assessing habitat destruction and biodiversity loss, but water is an issue far closer to most people’s daily experience … particularly in South Australia where the authors of this website live. You can’t usually see firsthand the water that goes into water-melon, beef or cheese production, but when water restrictions prevent you using a hose to water your garden, something serious is happening and everybody knows there is a problem.
Adelaide is at the end of the Murray river and is currently spending $1.8 billion on a desalination plant to supply 50 billion litres per annum. Our up-stream neighbours, the Victorians, took over 2,000 billion litres from the Murray Darling Basin in 2005-6. Still further upstream our NSW brothers and sisters took over 4,000 billion litres from the Basin in 2005-6. The Victorian figure is 34 times the capacity of the desalination plant. Hence, not much water gets into the river or is left in the river for us.
These massive off-takes were for agriculture, which is far and away the biggest user of water in Australia. Typically dairy farmers use flood irrigation to grow rich fodder crops to keep high yield dairy cattle well fed.
The off-takes from the river during a time of drought put the river under serious stress and by 2007-8, the irrigation use had dropped to just 1,400 billion litres for NSW and 937 billion litres for the Victorians. By this time, eco-system damage was well under-way with dead and dying trees and the impacts that has on birds and other animals. The big growth industry that was primarily responsible was the dairy industry which underwent massive expansion in the Murray Darling basin during the late 1990s. The dairy industry had a peak usage of about 4,200 billion litres in 2001/2.
Measuring water use
Water is constantly moving and measuring its use is tricky. Water that evaporates will eventually fall as rain, but it may be somewhere else so you have lost it. Water that seeps into the ground will eventually end up as usable groundwater but it will take time to reach the aquifers (underground geological structures) from which it can be tapped.
Scientists have a really clever way of measuring water in food production which gets around most of those measurement difficulties. Evapotranspiration estimates account for temperature, humidity, and the use of water during growth by plants. If you know how much of different foods are typically consumed by animals during the production of meat and dairy products, then you can give estimates for the amount of water used for those products. Here are some average figures independently calculated using these methods for Australian conditions:
|product||litres per kilo||litres per calorie|
The “litres per kilo” column of the above table comes from the report cited previously, the other column was calculated using the Australian and New Zealand Food Standards database. We could have added plenty of other columns to the table, a column for litres per milligram of vitamin C, folate, phytochemicals, fibre and so on. In most cases veggies and fruit would be the most water efficient source of nutrients. The veggies also come with far less or no saturated fat and other harmful substances found in cooked meat.
The above figures are an average. Figures on water use for fruit and vegetables are lower than grains as can be seen by the bananas and tomatoes figures. Interestingly, if you calculate the water used to produce a gram of protein from vegetables, it is much lower than even for grains. Do vegetables contain protein? Of course they do. Horses need protein, just like we do … and they get it from grass. You have to eat more vegetables to get the same protein as in a small piece of meat, but in doing so, by eating large amounts of vegetables and fruit, you get plenty of all the good nutrients that can protect you from cancer and other diseases. This is why diets with large amounts of meat are deficient in many useful nutrients while being over-supplied in a few like iron and protein. Most meat eaters eat far more protein than is recommended by Australia’s National Health and Medical Research council as the recommended daily requirement, with some people, particularly those on diets like the CSIRO Total Wellbeing Diet, eating more than the recommended maximum protein intake.
Irrigation water and rain water
The figures in the table above are actual water used in the plant or animal during growth and don’t take into account waste or whether the water is paid for or may have alternative uses. Typically, rice and dairy fodder crops are flood irrigated. This is highly wasteful, but farmers in both industries are actively working to reduce the amount of water they use. Wheat in Australia is largely grown with rain water which is why our yields are generally below the world average. Many beef cattle grow on what are called managed or improved pastures, they may even be “laser levelled” (deliberately flattened to ensure maximum water uptake — this also reduces the inflow of water into local rivers). CSIRO estimates of water used for rain fed grazing is much higher than the figures in the table for beef and can be as high as 50,000 to 100,000 litres per kilogram. Wool requires 170,000 litres for each kilo produced. Again this is water used to grow grass for sheep and which is therefore of reduced or no use to wildlife. Nobody pays for this water, it is an eco-system service, a product of the climate system.
The issue of water is very much a choice about our use of eco-system services. We can choose either to minimise our own use of water so as to maximise its availability for other species, or we can choose to maximise our appropriation.