You want things which will bring you pleasure and need things which will alleviate pain.
I want candy. I need water.
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Want
To desire greatly; wish for: They want to leave. She wants a glass of water. See Synonyms at desire.
To desire (someone to do something): I want you to clean your room.
To request the presence or assistance of: You are wanted by your office.
To seek with intent to capture: The fugitive is wanted by the police.
To have an inclination toward; like: Say what you want, but be tactful.
Informal. To be obliged (to do something): You want to be careful on the ice.
To be without; lack. See Synonyms at lack.
To be in need of; require: “‘Your hair wants cutting,’ said the Hatter” (Lewis Carroll).
Need
A condition or situation in which something is required or wanted: crops in need of water; a need for affection.
Something required or wanted; a requisite: “Those of us who led the charge for these women's issues... shared a common vision in the needs of women” (Olympia Snowe).
Necessity; obligation: There is no need for you to go.
A condition of poverty or misfortune: The family is in dire need.