Baptism is water and the word, but specifically in the name of the Father and of the Son and of the Holy Spirit. The amount of water is never indicated.
The Bible never says; it is completely silent on any mandated mode. It says "do" but not "in this precise way."
All Christians accepted this until some German extremists (Anabaptists) in the 16th Century insisted that there's a verse that says, "Thou shalt entirely dunk the recipient under water - every cell covered - or else it's not valid." They've had about 500 years to give us the reference for that verse but as of yet haven't done so.