First let me say that I do believe in infant baptism as the sign of the New Covenant, just as circumcision, the sign of the Old Covenant was performed on infants. However I do not believe that water baptism is necessary for salvation except in the sense that Scripture tells us to be baptized and we should follow God’s word.
This is what Scripture says about water baptism which is necessary for salvation;
1 Peter 3:18-21 (ESV)
18 For Christ also suffered once for sins, the righteous for the
unrighteous, that he might bring us to God, being put to death
in the flesh but made alive in the spirit,
19 in which he went and proclaimed to the spirits in prison,
20 because they formerly did not obey, when God’s patience
waited in the days of Noah, while the ark was being prepared,
in which a few, that is, eight persons, were brought safely
through water.
21
Baptism, which corresponds to this,
now saves you, not as
a removal of dirt from the body but as an appeal to God for a
good conscience, through the resurrection of Jesus Christ,
Navarre Bible Commentary:
The waters of the flood are a fugure of those of Baptism: just as
Noah and his family were saved in the ark from the destruction
wrought by the flood, now people are saved through Baptism,
by which they become members of Christ’s Church.
John 3:5 (ESV)
5 Jesus answered, “Truly, truly, I say to you, unless one is born
of
water and the Spirit, he cannot enter the kingdom of God.
Titus 3:5 (ESV)
5 he saved us, not because of works done by us in righteousness,
but according to his own mercy, by the
washing of regeneration
and renewal of the Holy Spirit,
I have a question for you. Do you believe we are stained by original sin? Do you believe in original sin? Whether you do or not, original sin exists, otherwise Jesus would not have to die for us. When we are born, we are born as sons & daughers of Adam. Baptism removes the stain of original sin, we are forgiven and therefore adopted by God. We do not become members of the Body of Christ unless we are baptized.
This is what the Catechism of the Catholic Church says about Baptism;
1213 Holy Baptism is the basis of the whole Christian life, the gateway
to life in the Spirit (vitae spiritualis ianua), and the door which gives access
to the other sacraments. Through Baptism we are freed from sin and reborn
as sons of God; we become members of Christ, are incorporated into the
Church and made sharers in her mission: “Baptism is the sacrament of
regeneration through water in the word.”
Please
read more here.