Obsessive-compulsive disorder: The affected person feels invaded by uncontrolled and repetitive thoughts, which cross their mind despite their desire or their will. The person is unable to stop having these thoughts, even though they usually know that they do not make sense. These thoughts then become obsessions.
Subsequently, the affected person may also have compulsions. They then feels compelled to repeat certain actions to chase the obsession from their mind or to reduce her anxiety. (Source Government of Quebec)

Obsessions with defilement are based on the fear and doubt of being defiled by the environment, both physical and mental. Often a washing ritual is associated, the water becoming a source of comfort; a sort of purification for "evil".
The images represent the mental state of the people affected by this disorder; the exhaustion they can feel from all the obsessions running through their minds.