Source : Webster's Revised Unabridged Dictionary (1913)

Dowser \Dows"er\, n.
   1. A divining rod used in searching for water, ore, etc., a
      dowsing rod. [Colloq.]

   2. One who uses the dowser or divining rod. --Eng. Cyc.

Source : WordNet®

dowser
     n 1: someone who uses a divining rod to find underground water
          [syn: {water witch}, {rhabdomancer}]
     2: forked stick that is said to dip down to indicate
        underground water or oil [syn: {divining rod}, {dowsing
        rod}, {waterfinder}, {water finder}]