The Collaborative International Dictionary of English v.0.48:

Water course \Wa"ter course`\
   1. A stream of water; a river or brook. --Isa. xliv. 4.
      [1913 Webster]

   2. A natural channel for water; also, a canal for the
      conveyance of water, especially in draining lands.
      [1913 Webster]

   3. (Law) A running stream of water having a bed and banks;
      the easement one may have in the flowing of such a stream
      in its accustomed course. A water course may be sometimes
      dry. --Angell. --Burrill.
      [1913 Webster]