Australia is the world's driest inhabited continent. Water is our limiting resource. It might therefore be thought that our water resources would be the subject of the most intensive study. Certain aspects, it must be conceded, have received much attention, notably the availability of water in terms of actual quantity. The size of the surface water and the groundwater resource is well understood and indeed receives about as much study as can reasonably be expected in a country with as sparse a population and level of scientific manpower as ours. Although the importance of understanding the...