SINGAPORE'S average annual rainfall is more than double that of notoriously soggy Britain, so the casual observer might be surprised to learn that the place has a shortage of drinking water. Yet with around 7,000 people per square kilometre, Singapore is the third most densely populated country in the world. Its land mass is not large enough to supply its 5m inhabitants with water.
One answer is to desalinate seawater. That, though, is expensive, so the Singaporean government is keen to find cheaper ways of doing it. And, in collaboration with Siemens, a German engineering conglomerate, it may have done so, for Siemens says its demonstration electrochemical desalination plant on the island can turn seawater into drinking water using less than half the energy required by the most efficient previous method.
To make seawater fit for human consumption its salt content of approximately 3.5% must be cut to 0.05% or less. Existing desalination plants do this in one of two ways. Some employ distillation, which needs about 10 kilowatt-hours (kWh) of energy per cubic metre of seawater processed. Other plants employ reverse osmosis. This uses molecular sieves that pass water molecules while holding back the ions, such as sodium and chloride, that make water salty. Generating the pressure needed to do this sieving consumes about 4kWh per cubic metre. The Siemens system, by contrast, consumes 1.8kWh per cubic metre,