"¿Cuánta agua necesitas?"
Translation:How much water do you need?
agua is feminine, but it's el agua rather la agua because agua begins with a stressed a sound.
I translated this as "How much water is necessary?" It said that this is incorrect. Can someone clear up my confusion? Thx
I went with something similar and also got it wrong - "How much water is needed?" The "you" seems to be necessary but I'm not sure why.
The difference is between active and passive voice. Active voice has a subject (a person doing something) while passive voice does not - it just states what is being done.
The phrase "How much water is needed" uses the passive voice, and is translated as "¿Cuánta agua se necesita?" or "¿Cuánta agua es necesitada?" Both of these are valid ways to say it, but I would use the first option ("se necesita"). (Note, I'm not a native speaker, and the preferred way to say it may vary from place to place; I'm not sure.)
I would personally translate "How much water is necessary" as "¿Cuánta agua es necesaria?", which also uses the passive voice.
"¿Cuánta agua necesitas?" has an implied subject (i.e. "¿Cuánta agua necesitas tú?"), and thus is in the active voice: it has a subject ("You") and the action that subject is doing ("need").
Necesitas means you need. How much water is necessary does not specify who needs the water while it clearly states in the question that the second person singular needs the water
"Necesitas" is singular second person familiar, so "you" must be included as the subject of the sentence: How much water do you need?/¿Cuánta agua necesitas? If the sentence had been third person singular, "¿Cuánta agua necesita?", then it could have been translated as singular "you" formal: "How much water do you need" or with the null subject (it)" "How much water is necessary?" The reason why is because "necesitar" means "to need." "Is necessary" and "is needed" are interchangeable in some English sentences, but not in all of them.
Necesitar is the verb to need. Cuanta agua es necesario would be how much water is necessary. Water would be the subject of the sentence in that case whereas 'you' is the subject in 'how much water do YOU need.