The Midrash (Bamidbar Rabbah 21:16-19) brings several proofs that Hashem doesn't need to eat, and therefore the passuk that states that the Karban Tamid is "my karban, my bread" (Bamidbar 28:2) is not to be taken literally. It should be obvious that Hashem doesn't need food, and there are pesukim to that effect (see Tehillim 50), but the Midrash seeks logical proofs that it must be the case.
To summarize these proofs:
- Hashem is merciful, and man is naturally cruel. Why would Hashem give His food to man, and leave His satiation to man to decide whether He eats?
- If karbanos are for our benefit, it makes sense why the only animals used as karbanos are domestic ones. If they are for Hashem's, why wouldn't He ask for a wild animal as a delicacy every now and then?
- If Hashem's shechinah is able to sustain others (malachim, Moshe Rabeinu), certainly He is able to sustain Himself.
- No creation requires its produce to survive. Likewise, Hashem doesn't require His produce (i.e. anything) to survive.
- A person needs to drink several handfuls of water. If the entire world's water can fit in Hashem's Palm (Yeshaya 40:12), there's no way we could give Him enough to drink - and certainly our measly little lug (Bamidbar 28:7) wouldn't be enough. Along similar lines, the Behemoth requires an enormous amount of water to drink. Hashem, in theory, would certainly require at least that much. Also along similar lines, Shlomo and Nechemiah had an enormous feast befitting of their stature. Hashem would be impossible to feed!
The second and fifth proofs seem awfully flimsy. The Midrash later (21:22) says:
One verse says (Iyov 37:23), "Shakai, He is not found full of strength," but it is [also] written (Iyov 36:22), "Behold, G-d is beyond reach in His power; who can rule like Him?" How can these two verses be reconciled? Rather, when He gives to [His creations], He gives to them according to His strength [and thus the verse in 36:22], but when He requests, He only requests according to their strength [and thus the verse in 37:23].
The Midrash proceeds to record several instances of this dichotomy.
Applying that to the earlier Midrash. Since Hashem only makes requests according to our means, of course He wouldn't ask us to go hunting for wild animals, or to feed Him the entire world's supply of water or food. How, then, can the Midrash claim that as a valid proof that Hashem doesn't need food or water? Perhaps He does, but, since He doesn't request beyond our means, He makes do with what He can?