Water is a recurrent symbol in the novel as a purifying element. This is seen when Raskolnikov goes back to his room and gets all of the stolen goods he has hidden. He plans to throw it all into the canal, but when he gets there, he walks up and down so long that people are beginning to notice him, and he decides not to throw the items in the canal. By throwing the stolen goods in the water, Raskolnikov thinks he can wash away all traces of his crime. He feels the water can wash away the blood stains, much as Lady Macbeth feels when she can't get the blood off her hands. Raskolnikov wanting to remove all physical evidence of his crime symbolizes his inner desire to cleanse his soul and his guilty conscience of the crime. Previously, Raskolnikov dreams of drinking clear, cool water from an oasis in the desert. Water in the desert symbolizes life, so Raskolnikov thinks by throwing the evidence of the crime into the water he will be able to get his own life back. He feels he lost his life when he killed the two women. Because he's unable to throw the items in the water, he admits that he can't get rid of the blood or his guilt.
Later, Raskolnikov stops on a bridge to look at the cathedral as it rises above the river. As he looks down into the water, he feels he's looking at his past life before the murders, and he knows he can never feel the way he did before he committed the murders. He throws the 20-kopeck piece into the water, cutting himself off from the world. Again, since the water is purifying, it is at this point that Raskolnikov feels he can never be cleansed of his evil crimes. He has given up on ever reclaiming his soul and ridding his conscience of the guilt he feels. He can never achieve redemption.
Water as a purifying element is also seen with Svidrigailov, who is afraid of water. He dreams of a young teenaged girl who committs suicide by drowning herself. She really killed herself by hanging, but Svidrigailov mixes up the circumstances of her death with his own. She killed herself because she had been sexually attacked, so the irony here is that the girl is innocent and he is depraved. Svidrigailov is surrounded by water everywhere, as it is raining and the cannons warn of a flood. His fear of water symbolizes his inability to seek salvation because he's already given up on himself. That's why he decides to kill himself.