This is the third question regarding these systems I am answering in the past few weeks. I am sure you can find my answers elsewhere on this site, but I will address the aspect of wasted water which you brought up.
While it is true that in the past water softeners were considered to be water wasters, and some still are, the better water softeners have become much more efficient over the past decade.
Utilizing new technologies such as demand-initiated regenerations, more advanced computer algorithms, and more efficient resins, water softeners have become very efficient. I will temper that statement with the following caveat: as long as they are properly sized and installed. Undersizing a softener will cause it to regenerate more frequently than is necessary.
It is for this reason that it is best to work with a reputable water treatment company, preferably one that has a Certified Water Specialist on staff. A company familiar with the water in your area will be able to recommend the right equipment after visiting your home and testing your water. What many people don't understand is that even though you can find softeners in any big box store, it is not always easy to find someone to properly install or service them.
In the long run, a properly sized water softener will not use too much water or salt and will protect your home's plumbing and water-using appliances as well as save money on things like soap and energy.
For more information:
Read Matthew O'Toole's Ask A Pro Q&A, "Which salt-free water conditioners will reduce scale?"