How much you want to bet the water company didn't know the chemical name of water is dihydrogen monoxide? Otherwise they could have explained to the callers that dihydrogen monoxide is, in fact, water and they were simply victims of an April Fool's joke. But that doesn't seem to be the path that was taken.
"Dihydrogen monoxide", shortened to "DHMO", is a name for water that is consistent with basic rules of chemical nomenclature, but is not among the names published by IUPAC and is almost exclusively used in humorous context.
