system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do nutrition labels even work?

I have a bottle of flavored water (0.68 cents at Wal-Mart, because I’m worth it) and it has 3 servings. If you drink 1 servings worth, you get exactly 0 calories and 0% everything else. But if you drink all 3 servings, you get 10 calories and about 10mg of sodium. How is that possible? I know there’s sometimes really small amounts of things like sodium, but isn’t that usually denoted as “<0%”?
gpt
If an item has less than five calories in it, it can be listed as "zero calories." In your example, the drink likely has about three calories per serving or something like that.

Basically, it's all round numbers, and the rounding can be weird sometimes.