In the book of John, Jesus had a conversation with a Samaritan woman at a well. During the conversation, Jesus spoke about living water, which refers to the Holy Spirit. He explained that whoever drinks of the water He gives will never thirst again and that it will become in them a spring of water welling up to eternal life. Therefore, when John says living water means water that wells up to eternal life, he is referring to the gift of the Holy Spirit that Jesus gives to those who believe in Him.