"So he sent two of his disciples telling them, 'Go into the city, and a man carrying a jar of water will meet you. Follow him. Say to the owner of the house he enters, "The Teacher asks: Where is my guest room, where I may eat the Passover with my disciples?" He will show you a large room upstairs, furnished and ready. Make preparations for us there.'" NIV translation
It was a Jewish custom that homeowners would make rooms available for anyone that came to celebrate the Passover and asked. Remember that the population of the city ballooned during the holidays and every room in the city would probably be used at this time. Jesus sent Peter and John to make the arrangements for their room.
There are those that say that Jesus must have met the homeowner before and made arrangements but this is not supported by the Scriptures. Jesus knew what was going to happen and even knew that they would see a man carrying water to lead them. He did not need to meet the man beforehand and make arrangements.
Another reason is that the disciples went with Jesus everywhere and, if He had already met this man and made arrangements, they would have known about the plans. If they would have known about the plans, then, they would not have needed to ask Him.
"The disciples left, went into the city and found things just as Jesus had told them. So they prepared the Passover. When evening came, Jesus arrived with the Twelve." NIV translation
It happened just as Jesus had told them and they must have been amazed. I cannot imagine what it was like to walk with Jesus and to physically see Him and have things like this happen. The closest thing we have is the Spirit living in us and that is great but this must have been so much more.
"While they were reclining at the table eating, he said, 'Truly I tell you, one of you will betray me - one who is eating with me.'" NIV translation
The traditional Passover meal was a special family meal and, here, we see that the great rejection includes one that was like family to Jesus.