Source : Webster's Revised Unabridged Dictionary (1913)

Backwater \Back"wa`ter\, n. [Back, a. or adv. + -ward. ]
   1. Water turned back in its course by an obstruction, an
      opposing current, or the flow of the tide, as in a sewer
      or river channel, or across a river bar.

   2. An accumulation of water overflowing the low lands, caused
      by an obstruction.

   3. Water thrown back by the turning of a waterwheel, or by
      the paddle wheels of a steamer.

Source : WordNet®

backwater
     n 1: a body of water that was created by a flood or tide or by
          being held or forced back by a dam; "the bayous and
          backwaters are breeding grounds for mosquitos"
     2: any backward region that is isolated from the world and
        resists progress