The Collaborative International Dictionary of English v.0.48:

Balneation \Bal`ne*a"tion\, n. [LL. balneare to bathe, fr. L.
   balneum bath.]
   The act of bathing. [R.]
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "balneation":
   Australian crawl, aquaplaning, aquatics, backstroke, bathe,
   bathing, breaststroke, butterfly, crawl, diving, dog paddle, fin,
   fishtail, flapper, flipper, floating, natation, sidestroke,
   surfboarding, surfing, swim, swimming, treading water, wading,
   waterskiing