When Jesus was baptized by St. John the Baptist, it wasn't just any body of water, or puddle, but the Jordan river. This is significant, as this spot wasn't random, but has profound biblical symbolism.
When the people of Israel were led to the "Promised Land," they had one final hurdle to overcome: the Jordan river.
The entire nation had to cross the Jordan river in order to claim the land that God had marked out for them. This action is narrated in the book of Joshua.
The people then followed Joshua across the Jordan river and were saved from their enemies and inherited the Promised Land.
Jesus is the New Joshua
Jesus' name in Hebrew is Yeshua, which is a form of the name "Joshua." Jesus then becomes the "New Joshua," leading the People of God across the New Jordan, through the waters of baptism.
The Catechism of the Catholic Church makes this connection explicit.
Jesus' baptism reminds us that everything is important in the Bible, even the most minute details of a location. It all points to deeper spiritual mysteries that are active in our own lives today.