Green’s Dictionary of Slang

(orig. N.Z.) a lavatory.

1934		J. Franklyn This Gutter Life 272: Ladies chatting on the doorstep about drain-’oles, dust-’oles and the ‘W.’.
1939		D. Thomas ‘Old Garbo’ in Portrait of the Artist as a Young Dog 197: ‘Got to go to the w. for a breath of fresh air’.
2003		McGill Reed Dict. of N.Z. Sl. 225: W The toilet, short for WC, which is short for water closet. Katherine Mansfield wrote of one in ‘Aloe’, 1916. Recorded here before elsewhere.