Heat the olive oil in a medium saucepan. Add the onion and cook over moderate heat until softened, about 4 minutes. Drain and quarter the artichokes; add them to the pan. Season with salt and cook, stirring, for 2 minutes. Stir in 1 tablespoon of the parsley, add the water and bring to a boil. Reduce the heat to moderately low and simmer until the artichokes are tender and most of the water has evaporated, 25 minutes. Transfer the artichokes and their cooking liquid to a bowl; season with salt. Sprinkle with the remaining tablespoon of parsley and serve.