I’ve written here on many occasions that not only is human wind and breathing far more important than the carbon footprint of travel vehicles: a much bigger problem is the lack of drinking water for a human population that has trebled during the last fifty years.

Only 0.7% of the water on earth is drinkable – and accessible. The average human being uses sixteen gallons a day. Already, 42% of the world’s population use less -not from choice, but from necessity caused by a lack of the stuff.

The biggest single problem is that nine tenths of all water is saline. As the ancient mariner remarked, ‘water water everywhere, and not a drop to drink’. Even worse, as the polar ice-caps are melting (and whether you believe the global warming doomwatch tendency or not, it is a fact that they are) sea levels must, over time, rise.

So here’s an idea that is no more or less economic or daft than extracting pollutant fossil fuels from under the seabed. Why not build a chain of desalination plants at each Pole – and then pipe the drinking water to all parts of the world?

It’s a six-pointer, as they say in Premiership soccer circles: more water to drink, and a gradual decline in (and then stabilisation of) rising sea levels.

I posted a Conundrum piece last night about why beer freezes after you take it from the freezer. This stimulated a vigorous debate about why melting ice caps raise sea levels – as a result of which I had this idea. It may be a crap idea; but what it proves yet again is that if you listen to people with another opinion – as opposed to yelling at them – the result may well be of benefit to everyone. The value of free speech is based upon this likelihood.

If this is a crap idea, please can people comment and tell me why.

Next week: how to halve the population growth without resorting to Nazi eugenics. (This is still work in progress).