The city councillors of Aliso Viejo in Orange County, California, are well-meaning, socially responsible people. And when they came across the huge threat posed to their constituents by dihydrogen monoxide they did what any elected official should do: they took steps to protect their community. A motion due to go before the city legislature proposed banning the potentially deadly substance from within the city boundaries.

Researchers found that the presence of dihydrogen monoxide in Aliso Viejo had reached startling levels: it was present in its crude form, often spilling unmonitored on to the city streets; it was found to be a crucial ingredient in many common chemical compounds; its presence was even detected in that most ubiquitous of civilised artifacts, the styrofoam cup.

And it got worse: dihydrogen monoxide is lethal if inhaled, causes severe burns in its gaseous state, and is the major component in acid rain. Prolonged exposure to solid dihydrogen monoxide can cause severe tissue damage. It can, said the city council report, "threaten human safety and health".

Fortunately for the concerned legislators, the rat was smelt before it got as far as the debating chamber. The perils of dihydrogen monoxide have been ignored until now largely because it is better known by its common name: water.

"It's embarrassing," said city manager David Norman in an inspired act of buck-passing. "We had a paralegal who did bad research."

The relieved styrofoam industry saw it as a sign of environmental correctness run wild. "The plastic industry has always been a favourite target of environmentalists," Robert Krebs of the American Plastics Council told the Los Angeles Times. "But we dream about instances like this when our opponents do something foolish."

So far, so amusing. But should this bout of crankiness be filed under Crazy Californians and their crazed correctness? Or is it another one to pin on that old bogeyman, the internet?

Certainly, California is a cranky place, cult centre of the universe, a self-made psychic at every corner. And correctness of all shades - political, environmental, whatever - can be exasperating and not a little hypocritical: in Los Angeles there is a surfeit of liquor stores yet the only thing anyone seems to drink is sparkling dihydrogen monoxide, and smokers are scared-looking furtive creatures, scurrying about from pavement to pavement, avoiding the disapproving stares of god-fearing, clean-living folk. LA is also a city where total strangers have no qualms about telling you just how you should be living your life, in the friendliest, most unassuming way possible.

The dihydrogen monoxide hoax is the result of a collaboration between the two prime suspects: a zealously concerned paralegal faced with an authoritative-looking spoof scientific website, dhmo.org, home to the Dihydrogen Monoxide Research Division. The Californian proactive social conscience - the social equivalent of current US foreign policy - combined with the influence of the internet was a recipe for confusion. The DHMO website professes to offer "an unbiased data clearing house and a forum for public discussion". "The success of this site depends on you the concerned citizen," says the introductory blurb.

It is, of course, absolute rubbish. But it is convincing rubbish, plausible because it feeds off and satisfies so many anxieties: about our environment, about science, about the unknown, about what we are doing to our bodies and ourselves. And in California, the environment, the unknown and, above all, the body - the, hairless, tummy-tucked body - are what count.