Australia should "rate" its food to show consumers how efficiently or inefficiently water is being used to grow it, an eminent CSIRO water scientist says.
Professor Wayne Meyer, Program Leader for Sustainable Agriculture in CSIRO's Land & Water division, says the heavy demands falling on the nation's water resources mean there must be greater scrutiny of how wisely Australia uses its water.
"We need to be more judicious about what foods we produce from limited water," he says.
"Making comparisons of water-for-food, or water-use efficiency, provides another piece of information to assess the balance between the need for economic productivity and protecting of the nation's water resource base."
For example, potatoes and sugar cane use about 60 litres of water per megajoule (approx. 240 calories) of food, compared with fresh apricots, grapes, cabbages and onions which use 160-200 litres.
To grow a kilo of dry wheat requires between 715-750 litres of water. For maize the figure is 540-630 litres. Rice needs 1550-2000 litres, while soybeans require from 1650-2200 litres to yield a kilo of dry beans.
The biggest users of water of all are meat and wool: growing kilo of beef requires 50,000 to 100,000 litres while a kilo of clean wool takes 170,000 litres of water.
If drainage and delivery losses are taken into account, these numbers are higher still, Dr Meyer says.
"People are often amazed at the volumes of water used for food production while others, like irrigated commodity groups, rally to defend and justify their use of water. This debate is welcome, because it heightens public awareness of the need for sensible use of our limited resources.
Dr Meyer say it is important to take into account the total water used, whether from rainfall or irrigation. This focuses attention on the water losses which occur through evaporation or drainage below the plant's roots.
"In dryland cropping, often only half the available water is used directly to grow the plant," he says. "The rest evaporates from the soil surface or sinks deep below the plant root zone.
"In irrigation, it can be even lower. Often, much less than 30 per cent of the water stored in a dam is used by the plants."
Overseas scientists have suggested that government subsidies on irrigation water should be removed to encourage farmers to use more efficient methods of water for growing crops. Dr Meyer believes this should prompt a wider water-for-food debate in this country.
"If Australia is to have an open and fully-accountable water system - ie water priced fully, with no hidden subsidies - the choice of crops which can be grown will be governed by the relative costs and returns for different enterprises."
The CSIRO scientist says Australia must eliminate unnecessary and unproductive losses of water and direct our research efforts to decreasing the amount of water lost for each kilo of protein produced.
Warning that little water remains to be harvested in mainland south eastern Australia, Dr Meyer says it is time to evaluate the use of irrigation for growing products such as meat and wool.
"It is not particularly sensible to use irrigation water exclusively to grow wool or meat. The large quantities of water needed to produces these things mean that only if water delivery is very cheap or wool or meat returns exceptionally high, will it be economically sensible in the long term."
He says irrigators must set gradually improving performance standards and foster a learning culture which embraces the transfer of their own know-how together with scientific and environmental breakthroughs.
"With global economic pressures and unwanted environmental consequences,
we simply cannot afford to use water on poor productivity and low return
Professor Wayne Meyer, CSIRO 02 6960 1562 (w)
015 953 544 (mob.)
Margaret Bryant, CSIRO Land & Water 08 93330615 (o)
08 9330 3101 (h).