All four Gospels mention water in relation to John the Baptist's ministry (1:26, 31, 33; 3:23); his was a baptism of repentance (Acts 19:4). Only John wrote of Jesus turning water into wine at the wedding feast in Cana (2:6, 7, 9, 4:6). Only John wrote of man's physical birth being one of water, as opposed to one being born of the Spirit (3:5). Only John recorded the Lord's conversation with the Samaritan woman at the well of Sychar (4:7, 10, 11, 13, 14, 15, 28). Only John discusses the lame man at the pool of Bethesda (5:3, 4, 7). Only John wrote of the Lord's disciples being filled to overflowing with the water of life: the Holy Spirit (7:38-39). Only John's Gospel tells of Jesus washing His disciples' feet (13:5). And finally, only John mentions the evidence of Jesus' death by the water and the blood which flowed from His side (19:34).
If one were to look at just these verses, I believe he could easily discern that Jesus was no ordinary man. He was faithful to the Law in His willingness to allow John to baptize Him. He was able to work miracles by changing water into to wine, and by healing the man at the pool of Bethesda. Jesus had wisdom far superior to other men, as can be seen in His teaching on sinners being born again, by His conversation with the Samaritan woman, and His understanding of the Holy Spirit's role in the lives of His disciples. He used the washing of His disciples' feet to show the humility He wanted His disciples to show toward others. And finally, and most importantly, John used the water which flowed from the spear wound, to prove that the humility of Jesus ultimately resulted in His willingness to die for us (see also Phil. 2:5-8).
While none of the Gospels mention water in relation to the Resurrection of Christ, it is the risen Christ who would fill His disciples with the Holy Spirit, and out of them, would flow the rivers of living water (compare 7:38-39 with Acts 1:5).
Our new birth takes place between the water of our physical birth,
and the water used as our testimony of being born again by our being baptized!