For Chayei Sarah
Not yet available on the Nishma website.
1) To answer the question of why the Magen Avraham simply distinguishes between food and water, I simply directed readers to Yad Ephraim, Orach Chaim 167:6, choosing, because of space limitations to not present his answer although, I would think, readers would like to know an answer to the question. What the Yad Ephraim basically states is that the obligation to feed animals first is -- derived, by the gemara, from Devarim 11:15 -- may be because God is only supplying us with food because of the needs of the animals. Our own merits, in themselves, may not be enough, ch'v'sh, to deserve the food. As such, we should feel the animals first. In regard to water, though, the providing of water is not dependent upon a perceived active involvement of God -- i.e. proper weather, etc. -- but is simply tied, in many ways, to what already exists -- wells, streams. As such, we do not have to water animals first.
You are invited to find other explanations.
1) An interesting question may exist in regard to Rav Moshe's answer. What if the person giving the charity states, as a condition of the charity, that the money should not go to one's animals. In the laws of tzedakah, a person giving charity can lay out certain conditions on how the recipient can use the money -- for example, a person can state that the money given cannot be used to pay off a debt. Could a person make a similar condition in regard to the tending of animals. If so, we could then simply argue that Rivka stated as a condition of her assistance that Eliezer must take water first -- and this would solve the entire question.