The following is largely from The Oxford Companion To Australian Literature:

Defined by the Macquarie Dictionary as 'a prudish teetotaller' or 'a killjoy' and by C.J. Dennis (read him for heaps of Aussie culture and folklore) as an 'ineffably pious person who mistakes this world for a penitentiary and himself for a warder'.

A term of uncertain origin, popularly accepted to be an acronym coined by by John Norton, owner of the (bloody marvellous, now defunct newspaper Truth) signifying "We Only Want Social Evils Remedied—or Righted".

Another suggestion is from "rouser" a term for religious fanatics current in Victoria in the 1870s.

The wowser had his heyday from the 1880s to the end of WW1 and was frequently depicted in cartoons as bearded, wearing a small, flat hat or a gimlet, and carrying the universal symbol of a wowser, an umbrella.

Rgds, lusy