Even if the world’s thirst for the dirty black stuff is eventually tamed, its craving for the clear blue stuff is on course to become a raging, insatiable monster. More agriculture, more pollution and a global population of 8.3 billion by the year 2525 should ensure that.

The question is whether the thirstiest nations will soon be held to ransom by the tankers and taps of the Organisation of Water Producing Countries (OWEC) — a swaggering, geo-politicised H2O equivalent of Opec in a water-starved global market.

And even if the concept of OWEC remains — for the time being — a figment of the imagination, it is significant to see whose imagination it has popped into. Intriguing research by the Nomura Research Institute (NRI) strongly suggests that Japan has done rather more than toy with the idea.

That direction of thinking is, of course, born of desperation. Throughout its modern industrial life, Japan has cowered at the mercy of the well mineralled. It may have crushed European electronics industries underfoot and left Detroit a foreclosed and rusting heap but, when it comes to oil, metals and food, it has unhappily played the addict, not the pusher.

That will not be the case, though, if water one day joins pork bellies, hot-rolled coil and West Texas Intermediate on the list of globally traded commodities. Give a barrel of water the same status as everything else that trades around the world, and suddenly Japan would find itself with a worthwhile spigot and a desirable raw material behind it.

At NRI, where researchers evidently entertain the idea of a global water market, calculations predict multi-billion dollar future income streams for Japan as the tables are turned on those nations it currently depends on for raw commodities. They plug a value of Y60 (30p) per cubic metre into their calculations. There is even talk of directly bartering shiploads of Australian iron ore or Dubai crude for vast tankers of Japanese water.

The idea depends on a strange but imminent shift in Japan’s landscape.

Until the vision of “Japan as water superpower” had been hatched, long-term population decline looked unremittingly bleak for the country. Japan’s birthrate is locked miles below replacement levels and the healthy diet has created a wave of retirees who can expect to live into their late 80s. The economists have wasted no time highlighting the probable effects of all this: industry will slow, consumption will collapse, tax burdens on the young will cripple and even the country’s famed powers of invention will eventually sputter.

But what never gets mentioned, and what NRI has spotted, is that this shrinking population and declining industrial base will consume far less water than it does today. Water companies around Kawasaki and Yokohama have already been forced to raise prices because use of the stuff has declined so sharply in recent years as homes and businesses have forced themselves to become more efficient consumers.

The NRI researchers suspect that, as the population of Japan continues its relentless decline, it will eventually produce an annual surplus of around 10 billion cubic metres of water suitable for drinking, agriculture or use in industry.

There is then the question of how that water reaches the places it is needed and might be purchased. Simple, say the NRI researchers: Japanese water is already heading around the world as wasted ballast in its ships. Conveniently, it is going to places that happen to be dry. Because Japan has no commodities to sell when it reaches, say, Australia or the Middle East, its iron-ore bulk carriers and crude tankers are filled only with water on their outward journey. The ballast water is dumped into the sea in a way that has caused huge concern to environmentalists.

But imagine if it were not, Japan is now wondering aloud: we could become troublesome, truculent commodity producers. If Canada became the Saudi Arabia of the brave new water-trading world, couldn’t we at least be Venezuela or Iran?

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