Water Baptism is a command to anyone who becomes born again.

Mark 16:15-16 says:

And he said unto them, Go ye into all the world, and preach the gospel to every creature. He that believeth and is baptized shall be saved; but he that believeth not shall be damned.

Baptism is a direct act of obedience to Christ's instruction. Baptism is not for church membership, but an open declaration of our new stand in Christ. When you are baptized you are openly declaring that you have by faith "put on Christ" so that men may see Christ in you. The lowering of the convert completely under the water pictures Christ's death; the submersion of the convert speaks of his burial and the raising of the convert from the water signifies his resurrection.

What is the Baptism of the Holy Ghost?

The baptism of the Holy Ghost is an experience the believer recieves after being "BORN AGAIN". It is a promise from God to all those who believe in Jesus Christ. One of the initial signs that you are baptized by the Holy Ghost is that you speak in tongues.

Acts 2:1-4

And when the day of Pentecost was fully come, they were all with one accord in one place....And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.

Anyone who is born again can receive  the baptism of the Holy Ghost with the evidence of speaking in tongues.