“I will sprinkle clean water upon you, and you shall be clean from all your uncleannesses, and from all your idols I will cleanse you. A new heart I will give you, and a new spirit I will put within you”
Short answer
The Church baptizes by immersion or by pouring water on the head, with the invocation of the Father, the Son and the Holy Spirit. She calls triple immersion the most expressive sign, because it shows burial and rising with Christ. She also holds that pouring is a true washing and has been accepted from ancient times. Older authorities judged sprinkling valid as well, but the Church's law names only immersion and pouring.
Drafted from primary sources. Every quotation is checked against the page it links to.
14 quotations in date order
“So those who received his word were baptized, and there were added that day about three thousand souls.”
“And he took them the same hour of the night, and washed their wounds, and he was baptized at once, with all his family.”
“Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, so that as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.”
“And concerning baptism, baptize this way: Having first said all these things, baptize into the name of the Father, and of the Son, and of the Holy Spirit, … in living water. But if you have not living water, baptize into other water; and if you can not in cold, in warm. But if you have not either, pour out water thrice upon the head into the name of Father and Son and Holy Spirit.”
“You have asked also, dearest son, what I thought of those who obtain God's grace in sickness and weakness, whether they are to be accounted legitimate Christians, for that they are not to be washed, but sprinkled, with the saving water. In this point, my diffidence and modesty prejudges none, … In the sacraments of salvation, when necessity compels, and God bestows His mercy, the divine methods confer the whole benefit on believers; nor ought it to trouble any one that sick people seem to be sprinkled or affused, when they obtain the Lord's grace”
“After these things, you were led to the holy pool of Divine Baptism, as Christ was carried from the Cross to the Sepulchre which is before our eyes. And each of you was asked, whether he believed in the name of the Father, and of the Son, and of the Holy Ghost, and you made that saving confession, and descended three times into the water, and ascended again; here also hinting by a symbol at the three days burial of Christ.”
“But with respect to trine immersion in baptism, no truer answer can be given than what you have yourself felt to be right; namely that, where there is one faith, a diversity of usage does no harm to holy Church. Now we, in immersing thrice, signify the sacraments of the three days' sepulture; so that, when the infant is a third time lifted out of the water, the resurrection after a space of three days may be expressed.”
“In the sacrament of Baptism water is put to the use of a washing of the body, whereby to signify the inward washing away of sins. Now washing may be done with water not only by immersion, but also by sprinkling or pouring. And, therefore, although it is safer to baptize by immersion, because this is the more ordinary fashion, yet Baptism can be conferred by sprinkling or also by pouring”
“Christ's burial is more clearly represented by immersion: wherefore this manner of baptizing is more frequently in use and more commendable. Yet in the other ways of baptizing it is represented after a fashion, albeit not so clearly; for no matter how the washing is done, the body of a man, or some part thereof, is put under water, just as Christ's body was put under the earth.”
“Although baptism can be administered validly by pouring the water or by immersion or by sprinkling, nevertheless, one should adhere to the first method or the second, or to the mixed form of these two, whichever is the more common practice and in harmony with the custom of the particular rite.”
“Baptism is to be conferred either by immersion or by pouring; the prescripts of the conference of bishops are to be observed.”
“Baptism is performed in the most expressive way by triple immersion in the baptismal water. However, from ancient times it has also been able to be conferred by pouring the water three times over the candidate's head.”
“The essential rite of Baptism consists in immersing the candidate in water or pouring water on his head, while pronouncing the invocation of the Most Holy Trinity: the Father, the Son, and the Holy Spirit.”