Lack refers to a deficiency, to the absence of something desirable, customary, or needful: "He feels a lack of confidence among his followers." "I am suffering from a lack of money and time." Want and need, as nouns, may have much the same meaning: "a necessity," "something that is required or demanded." One may say "My wants (or my needs) are few." Need has connotations that give it an emotional appeal (a need to be loved). Approximate synonyms for lack and want include dearth, scarcity, inadequacy, deficit, and insufficiency. Distinctions among these words when used as verbs can be suggested by these sentences: "These plants lack water." "These plants want water." "These plants need water." In the first sentence, lack suggests deficiency; in the second, want suggests desire; in the third, need implies necessity.
Dictionary of problem words and expressions. Harry Shaw. 1975.