The dihydrogen monoxide hoax involves calling water by the unfamiliar chemical name "dihydrogen monoxide" (DHMO), and listing some of water's effects in an alarming manner, such as the fact that it accelerates corrosion and can cause suffocation. The hoax often calls for dihydrogen monoxide to be regulated, labeled as hazardous, or banned. It illustrates how the lack of scientific literacy and an exaggerated analysis can lead to misplaced fears.
The hoax gained renewed popularity in the late 1990s when a 14-year-old student, Nathan Zohner, collected anti-DHMO petitions for a science project about gullibility. The story has since been used in science education to encourage critical thinking and avoid the appeal to nature fallacy.
A 1983 April Fools' Day edition of the Durand Express, a weekly newspaper in Durand, Michigan, reported that "dihydrogen oxide" had been found in the city's water pipes, and warned that it was fatal if inhaled, and could produce blistering vapors. The first appearance of the hoax on the internet was attributed by the Pittsburgh Post-Gazette to the so-called "Coalition to Ban Dihydrogen Monoxide", a parody organization at UC Santa Cruz following on-campus postings and newsgroup discussions in 1990.
This new version of the hoax was created by Eric Lechner, Lars Norpchen, and Matthew Kaufman—housemates while attending the University of California, Santa Cruz in 1989–1990, revised by Craig Jackson in 1994, and brought to widespread public attention in 1997 when Nathan Zohner, a 14-year-old student, gathered petitions to ban "DHMO" as the basis of his science project, titled "How Gullible Are We?"
Jackson's original site included the following warning:
A mock material safety data sheet—a list of information about potentially dangerous materials used in research and industry—has also been created for H2O.
The water molecule has the chemical formula H2O, meaning each molecule of water is composed of two hydrogen atoms and one oxygen atom. Literally, the term "dihydrogen monoxide" means "two hydrogen, one oxygen", consistent with its molecular formula: the prefix in dihydrogen means "two", the prefix in monoxide means "one", and an oxide is a compound that contains one or more oxygen atoms.