If this simple ritual doesn't appeal to you, many introductory books on paganism and several pagan web sites describe different methods of purifying an area before engaging in any magical work. If you do decide to keep a sacred space in a permanent and visible place, people will ask you about it. Be prepared to explain what it is and why you have it. If someone becomes hostile who does not live with you because of your beliefs and how you represent them, you might want to ask the person to leave before the tension ruins the calm of your dwelling. If your roommate is unwilling to let you have your space, you will need to work out a compromise with him or her, and you may have to simply give up having an altar.
Sacred space is important.
However, there are alternatives if you have to do without such an area for a period of time. Taking care of yourself and your safety is much more important than having a table for displaying candles and incense.