Why is there water in a coal mine? Does it affect the coal if its mine is wet?

Question: Why is there water in a coal mine? Does it affect the coal if its mine is wet?
- Keywords:
  coal mine,
  water,
  wet
Asked by woodpigeon to Rachel on 13 Mar 2013.
- Rachel Harris answered on 13 Mar 2013:
  
  As you dig into the ground to get your coal out you hit the natural ground water level. To keep the mine dry during operations the water is pumped out of the mine. Ice the mine is closed and the pumps are turned off the water fills back into the mine from the surround area.

Question: Why is there water in a coal mine? Does it affect the coal if its mine is wet?