Titus 3:5,6 He saved us through the washing of rebirth and renewal by the Holy Spirit, whom he poured out on us generously through Jesus Christ our Savior,Water has two primary functions. One function is to wash away things.
John 3:5 Jesus answered, "I tell you the truth, no one can enter the kingdom of God unless he is born of water and the Spirit.
John 4:14 whoever drinks the water I give him will never thirst. Indeed, the water I give him will become in him a spring of water welling up to eternal life.
Revelation 22:17 The Spirit and the bride say, "Come!" And let him who hears say, "Come!" Whoever is thirsty, let him come; and whoever wishes, let him take the free gift of the water of life.
Acts 22:16 And now what are you waiting for? Get up, be baptized and wash your sins away, calling on his name.That is the washing of rebirth. God wants us to be clean of sin. "that He might sanctify and cleanse her with the washing of water by the word, that He might present her to Himself a glorious church, not having spot or wrinkle or any such thing, but that she should be holy and without blemish." Eph 5:26,27
Such cleansing deals first of all with the forgiveness of sins, and then also it deals with cleansing one's sinfulness. Cleansing one's sinfulness involves changing one's behavior, one's sinful habits. That is the outside of the vessel. But more importantly it involves cleansing the inside of the vessel. The inside of the vessel are one's attitudes, values, innate desires of the heart and thoughts of the mind. The process of sanctification culminates in perfect sinlessness both external and internal. It incorporates the resurrection from the dead in which even one's physical body is transformed into a sinless vessel.
Another function of water is to give life. Indeed one cannot live without water for very long. Drinking water is not the same as washing with water. One does not think of drinking water to become clean. One drinks water because they are thirsty. The Christian life is not simply about having one's sins forgiven. Nor is it simply about not sinning. There is new life which God imparts through the Holy Spirit such that one is even spoken of as being born again, or born of the Spirit.
Life also begets life. Thus Christians will have spiritual offspring - future generations brought about by the Spirit of God. Life will spring up where there was no life.