Water softeners use a few different methods to operate, but essentially the equipment "exchanges" hard minerals for either sodium or potassium. According to the Water Quality Association, some equipment also may reduce levels of arsenic, nitrates and mercury.
Softeners are available in several sizes and are rated by the amount of hardness they can remove.
The downside to water softeners is the amount of sodium added to the water. That could be unsafe for some people, but typically, people like the taste of hard water much better than soft. As a result, cold water tap lines are usually purposely left unsoftened (although, not necessarily untreated).
The following products are just a few of the newest additions to the water softener market.