How was water used as an image in Act 3, scene 2 in Shakespeare's Macbeth?

Shakespeare uses imagery in his plays to add a deeper
meaning in his text.  The image of water for example (although it is not found in Act 3,
scene 2), represents innocence and the washing of guilt.  Traditionally, water is used
to wash oneself.  In baptism, the water is used to wash away original sin. 
Consequently, these images bring deeper meaning to the play.  After the murder to
Duncan, Macbeth is grief stricken and cannot believe what he has done.  In fact, Lady
Macbeth is forced to finish the job for him by smearing the bloody daggers on the
sleeping guards and framing them for the murder.  When she returns to her husband she
tells him, "A little water clears us from this deed."  By washing the blood off of their
hands (literally), Lady Macbeth is insinuating that they are also washing away the
guilt.  Unfortunately for her, at the end of the play, she realizes that washing with
water is not so powerful.  Her mind is so troubled at the end of the play that it
manifests itself through bouts of sleepwalking.  During these nightly episodes, she
re-enacts the murder of Duncan where she cannot remove the blood from her hands.  When
she repeats the words, “Out, damn'd spot!" she is realizing that her guilt cannot simply
be washed away.