The speaker is drinking to get away from suffering, but the poem suggests it doesn't quite work. The opening line, "Pain with pain, / water into water," sounds like an equation in which nothing is solved. Pain doesn't cancel pain; it just joins it, the way water poured into water simply becomes more water. The drink doesn't change anything, it only adds to what is already there.
The next lines turn this into an odd, almost playful image. The speaker has so much wine that they "water" themselves, as if they were a plant being soaked, or a drink being diluted. There's a sense of losing a firm sense of self, of being thinned out.
The ending is quiet and heavy. The speaker "hew[s]" a lodging in "a dark bed," a verb that suggests hard, deliberate labor, like carving out a shelter from stone. Judging by the imagery, this bed could be sleep, a place to hide, or something darker. The mood is weary, numb, and resigned, with a hint of grim humor.