What does Luke 22:10 mean?
Jerusalem is teeming with people; some estimates say hundreds of thousands. They have come to celebrate Passover. In a few scant hours, those people will sit at dinner with family and friends, eating roasted lamb, unleavened bread, and oil with herbs, and drinking wine. Jesus has decided it's time for Peter and John to prepare the meal for Himself and the twelve disciples (Luke 22:8).Peter and John trust that Jesus knows what they should do. Getting supplies shouldn't be a problem: the merchants are used to providing for all the travelers. Where to hold the dinner would be a problem if they didn't have Jesus.
Most homes in Jerusalem don't have their own water supply. Women are usually tasked with going to public fountains to draw water for the household, but sometimes male servants do, as well. The wording in Matthew 26:18 suggests that Jesus may have prearranged both the room and the meeting with the man, but it's unclear.
Regardless, Peter and John follow the man into a house in the city and tell the owner, "The Teacher says to you, Where is the guest room, where I may eat the Passover with my disciples?" (Luke 22:11). Peter and John follow Jesus' instructions and find things exactly as He had said.