And they said unto him, We can. Renewing brought about by the Holy Spirit gives a new life. The chosen People passed through the Red Sea when they left Egypt. In passing, they were not immersed in water. If anything, the clouds would have poured water on them, but, in fact, they passed through on dry land.
Various circumstances surrounding baptismal events strongly suggest pouring.
In the desert city of Jerusalem, it is unlikely there would have been a large body of water available to baptize the 3,000 except for the city water supply. There was not enough time to find enough water to immerse him in. Later Peter, through a vision and a call, went to Cornelius, a Roman centurion, and told him about Christ. Again we see the pouring out of the Holy Spirit linked to water baptism. The baptism here immediately followed the receiving of the Holy Spirit.