Learn Spanish (Latin America): Yo necesito una botella de agua.

No, you can simply say Necesito una botella de agua. In Spanish, the -o ending on the verb necesito already tells us that 'I' am the one needing it. Adding Yo just puts a little extra emphasis on who is doing the action.

Why do we use de here instead of just saying una agua botella?

In English, you can stack nouns together to describe something (like 'water bottle'). In Spanish, you can't do that. You have to connect them with the preposition de (of). So, you must phrase it literally as 'a bottle of water' (una botella de agua).

I learned that water is el agua. Why is there a feminine word like una in this sentence?

The word una (a) is feminine because it matches botella (bottle), which is a feminine noun. As a quick refresher, the word agua is actually feminine too! It only uses el instead of la (el agua) because it starts with a stressed 'a' sound, making la agua awkward to pronounce.

How would I say 'I need to' instead of just 'I need' using necesito?