Dihydrogen monoxide hoax
The dihydrogen monoxide hoax involves listing negative effects of water under an unfamiliar scientific name, then asking individuals to help control the seemingly dangerous substance (caused by most people knowing the word "monoxide" as part of the name of the poisonous gas "carbon monoxide"). The hoax is designed to illustrate how the lack of scientific knowledge and an exaggerated analysis can lead to misplaced fears. Dihydrogen monoxide, shortened to DHMO, is a scientific name for water that, while technically correct, is almost never employed.
The hoax was apparently created by Eric Lechner, Lars Norpchen and Matthew Kaufman, housemates while attending UC Santa Cruz in 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?"

# Original Web appearance
The first appearance on the web was attributed by the Pittsburgh Post-Gazette to the so-called Coalition to Ban Dihydrogen Monoxide, a hoax organization started by Craig Jackson following the initial newsgroup discussions.  The site included the following "warning":
Dihydrogen monoxide:
- is called "hydroxyl acid", the substance is the major component of acid rain.
- contributes to the "greenhouse effect".
- may cause severe burns.
- contributes to the erosion of our natural landscape.
- accelerates corrosion and rusting of many metals.
- may cause electrical failures and decreased effectiveness of automobile brakes.
- has been found in excised tumors of terminal cancer patients.
Despite the danger, dihydrogen monoxide is often used:
- as an industrial solvent and coolant.
- in nuclear power plants.
- in the production of styrofoam.
- as a fire retardant.
- in many forms of cruel animal research.
- in the distribution of pesticides. Even after washing, produce remains contaminated by this chemical.
- as an additive in certain "junk-foods" and other food products.
The original webpage is no longer accessible, but a October 31 1996 version has been mirrored by The Internet Archive.

# Terminology
"Dihydrogen monoxide" may sound dangerous to those with a limited knowledge of chemistry or who hold to an ideal of a "chemical-free" life. The term monoxide has negative connotations due to its being part of the name of the highly poisonous carbon monoxide.
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 di- in dihydrogen means "two", the prefix mono- in monoxide means "one", and an oxide is a compound that contains one or more oxygen atoms.
The use of numerical prefixes is typical nomenclature for compounds formed by covalent bonds, which are present in water. The prefix for the first named element is often dropped if the elements involved commonly form only one compound, or even if the number of atoms of the first-named element is the same in all the compounds of the two (or more) elements. Thus H2S is often simply called hydrogen sulfide, and lithium oxide is a common name for Li2O. However, the names dihydrogen sulfide, dilithium oxide, and dilithium monoxide are also commonly used both in industry and in universities.
The mono- prefix is often dropped for the second-named element if it is the only common compound the elements form. Thus for instance the IUPAC name of H2S is hydrogen sulfide rather than hydrogen monosulfide. However, since carbon and oxygen can form several compounds (carbon monoxide, carbon dioxide, tricarbon dioxide, and dicarbon monoxide), the mono- prefix is kept, as it is with silicon monoxide and silicon dioxide. Indeed, hydrogen and oxygen do form another common compound, H2O2. (Using prefix nomenclature, H2O2 would be called dihydrogen dioxidealso known as hydrogen peroxide.) Thus, keeping the mono- in dihydrogen monoxide does serve to distinguish it from another compound.
Water has a regular scientific or systematic name of hydrogen oxide, as well as an alkali name of hydrogen hydroxide and several acid names such as hydroxic acid, hydroxylic acid, and hydroxilic acid.  Incidentally, the term "hydroxyl acid" used in the original hoax is slightly incorrect, as it does not follow convention.  Additional names of -oxido dihydrogen and oxidane have been developed for this compound.
Under the 2005 revisions of IUPAC nomenclature of inorganic chemistry, there is no single correct name for every compound. The primary function of chemical nomenclature is to ensure that the person who hears or reads a chemical name is under no ambiguity as to which chemical compound it refers: each name should refer to a single substance. It is considered less important to ensure that each substance should have a single name, although the number of acceptable names is limited. Water is one acceptable name for this compound.  The other IUPAC recommendation is oxidane.

# Public efforts involving DHMO
- In 1989, Eric Lechner, Lars Norpchen and Matthew Kaufman circulated a Dihydrogen Monoxide contamination warning on the UC Santa Cruz Campus via photocopied fliers. The concept originated one afternoon when Matthew recalled a similar warning about "Hydrogen Hydroxide" that had been published in his mother's hometown paper, the Durand (Michigan) Express, and the three then worked to coin a term that "sounded more dangerous". Eric typed up the original warning flier on Matthew's computer, and a trip to the local photocopying center followed that night.
- In 1994, Craig Jackson created a web page for the Coalition to Ban DHMO.  The page spread widely on the net and off, including publication as an ad in a 1995 issue of Analog Magazine.
- The Friends of Hydrogen Hydroxide was created by Dan Curtis Johnson partly as a foil on the Coalition page, to provide evidence of 'misguided' supporters of dihydrogen monoxide. This form of collaborative connivance is a classic tool of internet spoofers.
- In 1997, Nathan Zohner, a 14-year-old junior high student at Eagle Rock Junior High School in Idaho Falls, Idaho, gathered 43 votes to ban the chemical, out of 50 people surveyed among his classmates. Zohner received the first prize at Greater Idaho Falls Science Fair for analysis of the results of his survey. In recognition of his experiment, journalist James K. Glassman coined the term "Zohnerism" to refer to "the use of a true fact to lead a scientifically and mathematically ignorant public to a false conclusion."
- In 1998, drawing inspiration from Jackon's web page and Zohner's research, Tom Way created the hoax website , including links to some legitimate sites such as the Environmental Protection Agency and National Institutes of Health.  Evaluating such sites can be instructive in developing critical thinking and information literacy skills.
- On April 1, 1998 (April Fools' Day), a member of the Australian Parliament announced a campaign to ban dihydrogen monoxide internationally.
- In 2001 a staffer in New Zealand Green Party MP Sue Kedgley's office responded to a request for support for a campaign to ban dihydrogen monoxide by saying she was "absolutely supportive of the campaign to ban this toxic substance". This was criticised in press releases by the National Party, whom 6 years later ironically had one of their MP's fall for the very same hoax.
- The idea was used for a segment of an episode of the Penn & Teller show Bullshit!, in which an actor and a camera crew gathered signatures from concerned environmentalists who wanted to ban DHMO.
- In March 2004, Aliso Viejo, California almost considered banning the use of foam containers at city-sponsored events because dihydrogen monoxide is part of their production. A paralegal had asked the city council to put it on the agenda; he later attributed it to poor research.  The law was pulled from the agenda before it could come to a vote, but not before the city received a raft of bad publicity.
- In 2006, in Louisville, Kentucky, David Karem, executive director of the Waterfront Development Corporation, a public body that operates Waterfront Park, which features a large, accessible public fountain, wished to deter bathers from using the fountain. "Counting on a lack of understanding about water's chemical makeup," he arranged for signs reading: "DANGER WATER - CONTAINS HIGH LEVELS OF HYDROGEN - KEEP OUT" to be posted on the fountain at public expense.
- An online petition to the British prime minister was correctly identified by the prime minister's office as a hoax, and rejected.
- In one episode of the children's science show How 2, Fred Dinenage used a glass of water in a perspex box to carry out the hoax, before drinking the water then explaining the truth.
- In 2007 Jacqui Dean, New Zealand National Party MP, fell for the hoax, writing a letter to Associate Minister of Health Jim Anderton asking "Does the Expert Advisory Committee on Drugs have a view on the banning of this drug?"