Scriptures: Mark 16:16 say he that believeth AND is baptised shall be saved but he that believeth not shall be damned. acording to the above scripture we can infer that baptism is a criteria. But the question was christ talking about water baptism?
Let's ponder together: when Jesus Christ was to be crucified he said to the thief at the right hand that surely today you shall be with me in paradise. In other words. That man made heaven without being baptised in water.
Many have argued that without water baptism a believer cannot make heaven. How true?

The saints that were waiting in abraham's bosom were not immersed. were they?
According to scriptures. There are three types of baptism. In heb 6:2 of the doctrine of baptisms... emphasis on the plural "baptisms.".
The first one being the baptism into the body of Christ. this type of baptism is what was referred to in mark 16. 16. We have to believe and 'accept' and be convinced and refute all old ways and be ready to live a new life. Remember the bible says if anyone be in christ he is a new creature.... This baptism of accepting jesus christ into our lives is what is expedient as believers.

The second baptism is the water baptism. Has written in the bible. This is by immersion. It is the physical demonstration of the spiritual it tells that u r physically renouncing the old ways and accepting the new one with men as your witness. When deeped into the water means being dead with christ, buried and resurrected with him. That was exactly what a believer also did when he repented and accepted Christ into his life. But this is the physical demonstration.
The third baptism is the baptism of the Holyghost. This baptism is done by christ on all willing and his disciples. In act 1:5 for John truly baptised with water. But ye shall be baptised with the holyghost not many days hence.

So the questions now is is water baptism what Jesus was referring to in mrk 16:16?
Where is the little lady that just accepted Jesus christ on her dying bed go? Where is the thief at the right hand of Jesus cross?

In romans 10:9-10 tells us the only way to salvation. ' If thou shall 'confess' with thy mouth the lord jesus and thou shall believe with thine heart that God raised him from the dead thou shall be saved. For with the heart man believes unto righteousness and with the mouth confession is made unto salvation.

Conclusion: water baptism is very good for believer but it is not a visa to heaven. It serves has a reminder to ailing believers. However the baptism into the body of christ by confessing his lordship is very necessary .