Jesus began his own ministry by coming to John to be baptized. It was pretty clear to John that Jesus had no need to be baptized for repentance of his sins. Indeed, John felt that Jesus should be baptizing him! Nevertheless, Jesus insisted John baptize him as a matter of righteousness being fulfilled by example in his life. (Matt. 3:13-15)
During Jesus' ministry he also baptized his followers, though it was his disciples who did the actual baptizing. Jesus' ministry, and his number of disciples and baptisms eventually outstripped John's. (John 3:22-4:2) In doing so, Jesus mandated the water baptism for all of his followers, including us.
Just as Jesus' ministry began with a declaration of the need for baptism, so it also ended. One of his last teachings before he left us included a command to "Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: Teaching them to observe all things whatsoever I have commanded you…." (Matt. 28:19-20a KJV)
So we continue to baptize believers with water in obedience to Jesus' word and in following the example of his life and ministry. And indeed it was one of the first acts of the new church. (Acts 2:41)