要 is extremely versatile: (1) 'want' — 我要水 (I want water); (2) 'will/going to' — 我要走了 (I'm about to leave); (3) 'need to/should' — 你要小心 (you need to be careful). The negative forms differ: 不要 (don't), 不想 (don't want to), 不用 (don't need to).
mistakes
不要 (bú yào) means 'don't!' (command). To say 'I don't want,' use 不想 (bù xiǎng) instead — it's softer and more polite.
