Wowser is a slang expression, most commonly heard in Australian and New Zealand English. It originated in Australia, at first carrying a similar meaning to 'lout', i.e. an annoying or disruptive person, or even a prostitute.
However, around 1900 it shifted to its present meaning: one whose sense of morality drives them to deprive others of their sinful pleasures, especially liquor. The term was particularly applied to members of temperance groups such as the antipodean branches of the Woman's Christian Temperance Union.
South Australians claim the term came from a temperance slogan there, "We Only Want Social Evils Remedied. However John Norton (January 25, 1858 - April 9, 1916), editor of the scandal-magazine Truth, claimed he first used the word in 1899 . "Wowser" was frequently used by artist and author Norman Lindsay, who fought many celebrated battles with "Wowsers" over the sexual content in his art and writing.
The Australian writer C.J. Dennis defined it thus: 'Wowser: an ineffably pious person who mistakes this world for a penitentiary and himself for a warder'.
Historian Stuart Macintyre argues, "the achievements of the wowsers were impressive;" they passed laws that restricted obscenity and juvenile smoking, raised the age of consent, limited gambling, closed down many pubs, and in 1915-16 established a 6pm closing hour for pubs, which lasted for decades.
Americans are likely to associate the word with H. L. Mencken:
'Wowser' is also the word given to describe a puritanical fanatic [US English]