The real question to ask is, "Do I need water treatment?" You probably do, since Houston was #6 on a list of the 10 worst cities in terms of water quality a couple of years ago (
http://www.dailyfinance.com/2011/01/31/ten-american-cities-with-worst-drinking-water/), but you can't just go buying a "system" without knowing what problem you're trying to solve. Houston, like all municipal water systems, publishes an annual water quality document that includes lots of contaminants, but doesn't include hardness, so you should test that yourself, then combine that with Houston's current report, and you'll know what you need to treat for. Judging from the 2011 report (Houston does an excellent job of hiding the 2012 report, if it's available), I would want to get rid of the chlorine (4ppm), just for aesthetic reasons.
Also, check to make sure Houston even allows you to do treat water yourself. Softening, in particular, is banned in some municipalities.