Actually it does. There are Bible verses justifying water baptism as necessary. In Mark there is a verse that says, "He who believes and is baptized shall be saved....." near the end of that book. And another in John where Jesus says, "Unless you are born of the water and the spirit you shall not see the kingdom of God....." Etc. But on the other hand, there seems to be verses that say that water baptism is not necessary to be saved. For example, there's that famous and often cited verse in Ephesians about how one is saved by grace through faith and not of works. And when Jesus was on the cross, he said to thief on the cross next to him that he would be in heaven with him today, which implied that one could obtain salvation without water baptism since that thief was not baptized. So this is an issue of debate between different Christian churches.
Actually you can find Bible verses saying a lot of things both ways. Pick and choose. As critics say, the Bible can be used to justify anything, even slavery. It's not a unified consistent book. It's written by a lot of people and says different things. It's an imperfect book and even honest Christians and Catholics today will admit that. The evidence is plain to see as long as you don't listen to fundamentalists.
I think officially the Catholic church did teach that water baptism is necessary to salvation and one of the seven sacraments. However the Catholic church has gone liberal since the 1960's and so all its traditional teachings are now in a gray area and the priests are trying to steer their teachings toward whatever is popular. Many Catholic priests nowadays even say that Satan or the devil doesn't even exist now, because that's the popular trend in New Age thought now. So they are conforming to the times and getting away from tradition and becoming more and more liberal. Now they are under pressure to let women be priests and to let priests marry, and to support gay rights, etc.