"How much water do you need?"
Translation:¿Cuánta agua necesitas?
"Agua" is femine (and not masculine). It takes "el" in the singular because of a clashing of vowel sounds, and "las" in the plural.
I'm not sure for un/una, but for other things like "esta" and clearly "cuánta" it goes to the feminine form (i.e. I can't describe the sounds to differentiate for myself but it is roughly the way it works)
Well, Spanish is a Romance language and most of its vocabulary is originated from Latin, which makes no sense as to being the cause of an exception. However, agua is not a masculine noun and just follows a rule where the feminine singular articles (la & una) cannot be used when the stress of a word beginning with a is on that beginning a. For example: El agua fría Las aguas frías Un agua fría Unas aguas frías
Why, though, when I tried this again, got the ¿Cuánta agua part right, and ended with "necesita usted?" did it object to my using the formal form of "you," and mark it wrong?
There is NOTHING about "how much water do you need" that either indicates, or would tend to MANDATE the sentence MUST use the informal "you" conjugation of "necesitar".
THAT should probably be fixed, or at least add an indication of which form, formal or informal, or when the singular or plural, is required. In English, "you" can mean any of many things and it's ambiguous. Formal or informal, (or familiar and polite, if you prefer,) and it's also both singular and plural. Spanish has at least about a half dozen words that all translate as "you" and are NOT interchangeable:
Tú: you (sing. fam.) Usted: you (sing. pol.) Ustedes: you (pl. pol.) Vosotros: you (pl. exclusively masculine, or mixed m/f, fam.) Vosotras: you (pl. exclusively fem., fam.) - Yeah, I know not all dialects use vosotro/as -
There may be others... I am not as yet fluent en español... not even close.
It's the achievement level you've reached in that language module.
I may be overanalyzing and that's why I'm getting stuck. But, in a different problem it was saying to move the verb to the beginning. For example:
How much does costs? Cuanto cuesto _
So how do I know when to shift the verb in a question or leave it where I hear it in English?