In general:

If a dream is about how the dreamer is submerged in the water, this usually indicates how he deals with his feelings. He tries to find the innocent part of his personality, which must not be affected by external circumstances. He tries to clarify situations and to clean himself – perhaps from ideas and settings, which were suggested to him by other people.

Psychologically:

If the dreamer has completely submerged in the dream (that is is completely concentrated), then this refers to the fact, that he is able to set the position, that directs all force of his whole thoughts, to see even more clearly on a particular idea.

Spiritually:

Transformation and rebirth can be completed only by total immersion in spirituality.