The global water crises has received substantial attention from international institutions such as the United Nations, governments, scientists, and more recently, the press. The UN Water Development Report projects that nearly 2.8 billion people live under conditions of severe water stress, defined as consuming 75% of total available renewable water resources. While desalination increases the amount of water available to populations by making non-potable water usable for human consumption and other needs, detractors decry the environmental ramifications (carbon footprint) of energy consumption used to desalinate water.

Given the energy numbers and related concerns bandied about, it is useful to consider the most extreme scenario where all of the world’s water needs – 4.2 trillion m³/year in 2008 – is derived from desalination. Typical seawater reverse osmosis (RO) desalination requires 3.5 kWh/m³, implying a total energy consumption of 14.7 trillion kWh/year if all water for human consumption including agriculture, cooling water for power plants, industry, and personal consumption were derived from the sea. This represents 11% of the 140 trillion kWh of primary energy consumed by the globe in 2008, or 27.5% if the primary energy used to generate the electricity for RO is included. Of course, this figure represents the use of present RO technology. RO is slated to reduce energy intensity by 30% within the next 10 years and alternative desalination methods, such as the forward osmosis process in development by Oasys, promise to use waste heat to drive desalination and bring the net energy consumption down by an order of magnitude (see also the report “Desalination’s Future Champions“). Alternatively, water reuse uses approximately one fifth the energy required by seawater desalination by virtue of a far reduced concentration of salts and other molecules that need removal. Given these improvements, it’s conceivable that all the world’s water needs could be met via desalination with as little as 5% of global energy consumption.

In short, in the very unlikely situation where all the water needs for humanity were derived from manufacturing water from the sea, only a fraction of the present world’s energy consumption would be required. While 5% is hardly a trivial figure, from an energy standpoint alone, it is eminently doable. That’s not to say that measures to improve water efficiency should be neglected; however, the exercise does serve to demonstrate the relative scale of energy required to desalinate water to overall energy consumption and demonstrates that the concerns over the energy intensity associated with desalination is overblown. For much more on the overlap between water and energy, look for an upcoming Water State of the Market report on this topic.

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