What does John 4:13 mean?

Here Jesus begins to unpack the concept of the "water of life." It was common for people to misinterpret Jesus' parables or teachings in a purely physical way. In some cases, those hearing Jesus sensed He wasn't being literal but could not see the point of the analogy (John 3:3–4). In others, they mistook the intended lesson (John 2:19–21). Jesus starts by explaining the difference between the literal well water, meaning the physical world, and living water, meaning the Holy Spirit. This is a concept Jesus will return to, in a much more public way, later in this gospel (John 7:38–39).

No matter how hard we try, earthly things will never satisfy the natural human longing for God. Writers from Augustine to C. S. Lewis have noted that human nature finds itself ultimately dissatisfied with material things. We seek those kinds of "water" because we're trying to quench our spiritual thirst. Only a healed relationship with God, through salvation in Christ, can solve that problem.