Next to air, fresh water has been always considered as the most important resource, central to economic development as well as to human physiological needs. Currently the total world population is about 7 billion, and, by 2050, it is projected to be 9 billion. By that time an additional 40 Nile Rivers will be needed. Historically, inland dams have successfully solved the water deficit problems in many places, but more and more countries are resorting to emerging technologies like desalination, wastewater recycling and rainwater tanks which are needed to replace inland dams for a number of geomorphological, environmental and societal reasons. These new technologies require a paradigm shift in the water supply industry: global water consumption is only 5~6% of annual runoff-as it is in Australia-so the coming shortage is not of water, but of storage.
A coastal reservoir is a reservoir designed to store floodwaters in a seawater environment. The first generation of this technology has been successfully applied in China, Singapore, Hong Kong and Korea, but the water quality is generally not as good as that from inland reservoirs. The second generation of coastal reservoirs has been developed and its water quality is comparable with the water available from conventional urban water supply reservoirs. The conceptual design of coastal reservoirs for Australia's capital cities is outlined.