Catechism of the Catholic Church §2652 — excerpt
The Holy Spirit is the living water "welling up to eternal life" in the heart that prays. It is he who teaches us to accept it at its source: Christ.
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.