Water

It kind of depends on what you're trying to achieve - you can decide on the method that helps you with your goals.

Pretty much any non-alcohol fluid is hydrating: That's what our body counts. That would include water, tea, coffee, the fluid part of soup/fruits/other foods, soda/pop, most of juice, even the non-alcohol part of beer or wine . . . you get the idea. If we get enough of those so that our urine is pale yellow, not dark and not clear, that's pretty much what we need. (It may even be bright almost day-glo yellow but still light, if we've gotten more than we need of certain water-soluble vitamins, and that's still OK.)

Probably obviously, I would only log most of those things as foods, not water . . . pretty much all of the ones that have calories, and certainly the ones that have other important nutrients.

Here's where IMO some personalization might come in: If a person were trying to drink more water and less of say zero-calorie soda/pop, it might make sense to log the water as water, and maybe set up a custom-named meal slot for the pop, so it would be possible to track one against the other. However, if a person were just under-hydrated, and wanted to be more so, it might make more sense to log water and zero calorie beverages in the water section, so all the non-nutritional hydrating liquids would be in one spot.

There's not an official set of rules to follow. We can do what best helps us meet our own personal goals for improving our health.