Learn German: Haben wir genug Wasser? - Do we have enough water?

Haben matches the subject wir (we). For the plural pronouns wir (we) and sie (they), as well as the formal Sie (you), the verb haben (to have) takes the form haben.

Where is the word for "Do" in this question?

German doesn't use helper words like "do" or "does" to ask questions. Instead, you just swap the subject (wir) and the verb (haben). So, the statement "We have" is Wir haben, and the question "Do we have?" is simply Haben wir?.

Why is there no word for "the" (like das) before Wasser?

Just like in English, you don't need an article for uncountable things (like liquids or materials) when you are talking about an unspecific amount. You say "enough water", not "enough the water". German does the exact same thing: genug Wasser.

Why is the word Wasser capitalized in the middle of the sentence?

In German, every single noun (a person, place, thing, or idea) is capitalized, no matter where it appears in the sentence. Since Wasser (water) is a noun, it gets a capital W.