The carafe of water

One of the eternal questions that plagues me here in Paris is the question of the carafe of water. Why is it that every time I order une carafe de l'eau I stand a roughly 30% chance of getting it? And why is it that whenever a French person seems to order absolutely anything — even just a tiny coffee — they seem to get a liter of water alongside? Why? My food comes. My wine comes. But hardly ever do I get the water without repeating my request several times. I am now practicing how to say, "Monsieur, I am dying of thirst. The carafe, please!" in French. Is this some secret way for the French to stick it to me while still being polite?