...is baptism is our rebirth/recreation and the Bible always associates creation/recreation with water.
in the very beginning God created the dry land by making the waters go
down and he made a covenant with Adam & Eve. In Noah's time God
recreated the world by flooding it with water and letting the waters go
down until dry land appeared. Only those in
the ark were saved and God made a new covenant with them. In the time
of Moses the Israelite people fled Egypt through the Red Sea; the waters
parted and dry land appeared. The Egyptians entered the waters and
drowned while the Israelites passed through and were saved from the
Egyptian army. On the other side, God called them his chosen people and
made yet another covenant with them.
Again and again we forces
of sin perishing in the waters and those who trust in God emerging a
new creation, free from sin and chosen by God. How odd would it be to
now say all we must do is recite a prayer for the same effect? In
baptism we believe sin is put to death inside of us and we emerge a new
creation chosen by God and part of his new covenant. This is yet
another reason Catholics use water in baptism.