Drowning is the central image here, and it stands for depression and self-destructive habits. The speaker feels weighed down, always longing for the surface. Drink or self-harm seem like the only ways to catch a breath, but the relief doesn't last, and they sink back to the bottom while the tiles "scream," as if the pool itself were closing in.
Then the poem shifts toward hope. The speaker imagines waiting instead of reaching for the bottle or blade, and eventually leaving the water for dry land. Rain still returns now and then, a reminder of the pool, but the speaker resists their vices and the rain passes. By the end, the mind is sunny, and the final line carries the poem's quiet confidence: even if the water comes back, they now know how to swim. The mood moves from suffocating and desperate to calm, steady and hard-won.