要
yào
Auxiliary verb "yao" and its multiple meanings
要 covers wanting, needing, ordering and the near future — the noun or verb after it decides which.
要 + Noun / 要 + Verb
How it works
With a noun it's "I'll have": 我要一杯水. With a verb it can be intention (我要走), obligation (你要小心) or prediction (要下雨了).
It also states requirements: 去中国要签证 — going to China requires a visa.
In practice, context does all the disambiguating, and native speakers never notice the ambiguity.
Examples
wǒ yào yì bēi shuǐ
我要一杯水。
I'll have a glass of water.
nǐ yào xiǎo xīn
你要小心。
You need to be careful.
qù zhōng guó yào qiān zhèng
去中国要签证。
You need a visa to go to China.