The book of Acts shows several examples of believers becoming Christians. In every case, water baptism was the final step for their salvation.
||Then Peter said to them, "Repent, and let every one of you be baptized in the
name of Jesus Christ for the remission of sins; and you shall receive the gift
of the Holy Spirit....Then those who gladly received his word were baptized; and that day about three
thousand souls were added to them....And the Lord added to the church daily those who were being saved.
||But when they believed Philip as he preached the things concerning the kingdom
of God and the name of Jesus Christ, both men and women were baptized. Then Simon himself also believed; and when he was baptized he continued with
Philip, and was amazed, seeing the miracles and signs which were done.
||Now as they went down the road, they came to some water. And the eunuch said,
"See, [here is] water. What hinders me from being baptized?" Then
Philip said, "If you believe with all your heart, you may." And he answered and
said, "I believe that Jesus Christ is the Son of God." So he
commanded the chariot to stand still. And both Philip and the eunuch went down
into the water, and he baptized him. Now when they came up out of
the water, the Spirit of the Lord caught Philip away, so that the eunuch saw him
no more; and he went on his way rejoicing.
||Immediately there fell from his eyes something like scales, and he [Paul] received
his sight at once; and he arose and was baptized.
||"Can anyone forbid water, that these should not be baptized who have received
the Holy Spirit just as we have?" And he commanded them to be
baptized in the name of the Lord. Then they asked him to stay a few days.
||And when she and her household were baptized, she begged [us,] saying, "If you
have judged me to be faithful to the Lord, come to my house and stay." So she
||And he took them the same hour of the night and washed their stripes. And
immediately he and all his family were baptized. Now when he had
brought them into his house, he set food before them; and he rejoiced, having
believed in God with all his household.
||Then Crispus, the ruler of the synagogue, believed on the Lord with all his
household. And many of the Corinthians, hearing, believed and were baptized.
||Then Paul said, "John indeed baptized with a baptism of repentance, saying to
the people that they should believe on Him who would come after him, that is, on
Christ Jesus." When they heard this, they were baptized in the name
of the Lord Jesus.
||'And now why are you waiting? Arise and be baptized, and wash away your sins,
calling on the name of the Lord.'