The Collaborative International Dictionary of English v.0.48:

Abstainer \Ab*stain"er\, n.
   One who abstains; esp., one who abstains from the use of
   intoxicating liquors.
   [1913 Webster]

WordNet (r) 3.0 (2006):

abstainer
    n 1: someone who practices self denial as a spiritual discipline
         [syn: abstainer, ascetic]
    2: a person who refrains from drinking intoxicating beverages
       [syn: abstainer, abstinent, nondrinker] [ant:
       drinker, imbiber, juicer, toper]

The Devil's Dictionary (1881-1906):

ABSTAINER, n.  A weak person who yields to the temptation of denying
himself a pleasure.  A total abstainer is one who abstains from
everything but abstention, and especially from inactivity in the
affairs of others.

    Said a man to a crapulent youth:  "I thought
        You a total abstainer, my son."
    "So I am, so I am," said the scapegrace caught --
        "But not, sir, a bigoted one."
                                                                  G.J.