Commentary for Genesis 18:4

יקח נא LET BE FETCHED, I PRAY THEE — This implies bringing by a messenger: therefore did the Holy One, blessed be He, recompense his (Abraham’s) children by a messenger when they required water, as it is said, (Numbers 20:11) “And Moses lifted up his hand and smote the rock etc.” (Bava Metzia 86b)

יקח נא מעט מים. "Let a little water be brought." Perhaps the reason Abraham spoke about a "little" water was to indicate that it was not much of an effort to procure it. He certainly was not miserly. Apparently, he did not want to depart from his custom to ask guests to wash their feet to remove the dust that most of them worshipped (Baba Metzia 86). [The author felt the need to justify the custom seeing Abraham was already aware that his guests were angels and not given to worship the dust. Abraham may not have wanted his servants to realise that his guests were angels. Ed.]

יקח נא מעט מים, the reason why he mentioned “a little,” is in order to understate his generosity, something that is expected of any person who claims to possess a certain minimum of good character traits. When referring to the water,” Avraham used the passive form of yukach, meaning the water would be supplied by someone other than himself, whereas when he spoke about the bread he would supply, he said: “I will take a piece of bread, etc.”