Jesus said to the servants, “Fill the jars with water”; so they filled them to the brim.
John relates that they were filled to the brim. This proves that there could be nothing added to them; the transformation of the water into wine was truly a miracle.
Jesus did not pray for the water to be changed into wine and He didn’t lay His hands on the jars. In fact, He didn’t do or say anything to cause the miracle to happen — He just willed it into being, proving that He is the Son of God.