Catechism of the Catholic Church §1228 — excerpt
Hence Baptism is a bath of water in which the "imperishable seed" of the Word of God produces its life-giving effect. St. Augustine says of Baptism: "The word is brought to the material element, and it becomes a sacrament."
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: St. Augustine, In Jo. ev. 80, 3: PL 35, 1840