The Gemarah (Taanis 9.) Says that one can find a hint for everything in the Torah. When the three Malaachim dressed up as Arabs, came to Avraham Avinu he provided them with a high class meal. Each one got the whole tongue of a cow with mustard, eight kilo of bread and much more. Our Rabbis say that every action Avraham Avinu did had ramifications on his grandchildren, the Jews, in later generations.
The Gemarah (Bava Metzia 86:) writes that Avraham Avinu did not himself bring water to his guests, but asked one of his helpers to bring them water. The Passuk says 'Yukach na me'at mayim'- a little water should be brought. The Gemarah says that although Avraham Avinu's Hachnasas Orchim was exemplary, but it was missing perfection due to the fact that he never brought the water himself. In return, when the Jews were in the desert, Hashem Himself didn't provide water directly but provided water via Moshe. (Although it was not a punishment, however, sadly, this caused tragedy, when Moshe struck the stone and didn't speak to the stone, Moshe was punished and didn't merit to enter Eretz Yisrael! Had Moshe entered Eretz Yisrael, he would have built the Beis Hamikdash and it would never have been destroyed!)
We see that the smallest actions of Avraham Avinu had massive ramifications for Klal Yisrael. If so," asked Rav Ovadia Yosef, "we need to understand something. Avraham Avinu sent a helper to bring water. For that Moshe provided the water and not Hashem himself directly. But Avraham Avinu sent a helper to bring only a little bit of water as it says in the Passuk 'me'at mayim' - a little water. We don't find that the Jews only had a little bit of water in the desert. In fact we find just the opposite, the wells of water in the desert were so big that in the Tosefta (Sukkah 3,3) tells us that boats could sail in both directions side by side in the water the Jews had to drink in the desert."
"The answer is, that if Avraham Avinu was using someone else to bring the water, he didn't want to overload him. Hachnasas Orchim, whatever Avraham Avinu did himself was plenty, but the water that someone else had to carry, he asked him to bring only a little bit! Chessed, yes; but not at the expense of others.
