What encouraging but mysterious revelation from Jesus. One, of course, might consider this in rather simple terms and not as terribly mysterious: helping others is a good thing and God rewards this. Giving water to the thirsty is a good thing. This is true, but there can be a temptation to reduce the Christian life to being good, and God sprinkling blessing atop our goodness, our good actions-like sprinkles on an icecream Sundae.
I am inclined to ask if Jesus is revealing something else, something more. Is Jesus not, in fact, revealing his "identification" with the thirsty? I recently saw a bumper sticker that I found clever and liked: "It's not a religion, it's a relationship". Indeed. The reward that God always ultimately gives is Himself. The reward that awaits us in giving water to the thirsty is an encounter. Jesus awaits us-and, this is mysterious.
I might do best simply to let Mother Teresa say it:
Seeking the face of God in everything, everyone, all the time, and his hand in every happening; This is what it means to be contemplative in the heart of the world. Seeing and adoring the presence of Jesus, especially in the lowly appearance of bread, and in the distressing disguise of the poor.
With you, finding Jesus in all sorts of places and all sorts of people,