THE idea of towing icebergs from the Arctic or Antarctic to supply fresh water to consumers is an old one, first proposed as long as half a century ago, but it has widely been rejected by scientists as technically implausible at a realistic cost.

John Isaacs, of the Scripps Oceanographic Institute in La Jolla, California, calculated in the 1950s that a fleet of six tugs would be able to tow an iceberg to his state’s coast in a few months.

A similar project was proposed by Prince Mohammed al-Faisal of Saudi Arabia in 1977, to resolve the oil-rich country’s water shortage.

It is practical to tow an iceberg using tugs: the exercise was first demonstrated off the coast of Newfoundland in 1971. It is sometimes performed to clear shipping lanes or to deflect large icebergs on a collision course with oil platforms.

However, iceberg-towing as a means of supplying fresh water has always foundered on the inefficiency of moving vast masses of ice over long distances.

Scientists have calculated that about 80 per cent of the mass of an iceberg would be lost on the journey, making the water that it would yield at its destination prohibitively expensive.

Cloud-seeding is another concept that has its historical roots in the 1950s. It involves dropping or shooting into the air fine particles, usually of silver iodide, which have a similar crystalline structure to ice. This encourages supercooled liquid water in the air to form ice crystals, which build up clouds and eventually induce rain.

The technology has been used with some success, particularly by the former Soviet Union to clear the skies before important communist parades.

It was also attempted by the governments of Malaysia and Indonesia last year to calm the forest fires that released a dangerous smog over South-East Asia.

It is a feasible method of increasing rainfall, but the technique is notoriously un- reliable. It does not always work, and some scientists argue that it does not produce any overall increase in precipitation. Cloud-seeding has also occasionally been blamed for inducing abnormally severe weather.

The most practical method of increasing the supply of fresh water in the South East of England is likely to be carrying it by tanker from Scotland or Scandinavia.

Although this is an expensive method, sea transport of very heavy bulk commodities such as water is the cheapest way of moving them around to where they are needed.

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