Everything period is a luxury, then. I mean, at which point do you draw the line between luxury and necessity? Okay, hot water is a luxury. What about running water? Clean water? Enough water to clean yourself? Enough water to avoid poor health?
Therefore, we can know a want from a need because a need is anything that if you were to go without it, would result in your death or stunted growth.
This piece, like Walden, is about how we can trade what we have mistaken for physiological needs for legitimate psychological needs.
Drawing on what aspirant said, Maslow's hierarchy of needs is a very good way to provide that context: at the level of physiological needs, you can consider "safety" level needs as "luxuries"; on the other hand, you would consider them as "necessities" from the "love/belonging" level.