Need is very essential for us, for example, air with oxygen to breathe, food to eat, sleep etc.
Want is something I desire to have, it could be a “need” or not. For example, if I am in short supply of air to breathe, I not only need it, I also want it. But wants tend to go beyond need, and our own attachment to our want makes it sound like a need. For example, one may want to have a drink to relax and recoup, but the attachment to the drink makes one feel to say, “I need a drink”. When a “need” also becomes a want, it is a genuine lack of privilege in life, for example a poor person wants to have food as she or he is quite hungry and can’t afford to have food.
When a “want” also becomes a “need”, it is a craving towards addiction, may be mild and it may not be a big deal. We need to watch on both our needs turning into wants and our wants turning into needs, both are unfortunate situations we do not deserve to have.