La Maison en Petits Cubes

An old man lives in a town that has become submerged in water. As the water rises, he's forced to build additional levels onto his home with bricks in order to stay above water. One day the old man accidentally drops his favorite pipe into the lower levels of his home, and decides to rent scuba diving equipment in order to go searching for his pipe. As he descends through his sunken home, the old man recalls memories of the past in each room.

Synopsis from Anime News Network