One of the questions many people have about water softeners is if the sodium added to the water will be unhealthy for people who have to have very low-sodium diets. Water softeners really don't add all that much sodium per cup of water, but for those who really need to cut out as much salt as possible, even a small amount in a cup of water can add up.
One solution that sites often suggest is to get a potassium-based water purification system. Another, however, is to look at water conditioning systems, also called salt-free water softeners. Both systems work to reduce the scale you see on glasses and showerheads, but they do it in different ways and with somewhat different total results.
Water softeners are meant to soften hard water that's filled with calcium and magnesium. The result is water that has more sodium and potassium, and that deposits less scale in areas like your shower. However, these softeners often don't remove scale from places like the water heater. Softeners use an ionic exchange to remove minerals.
Conditioners, though, can modify the scale-causing minerals through chemical transformation, and they are also better at getting the scale out (or rather, preventing scale from settling in) places like the water heater. The conditioners remove minerals but don't really replace them.
On the surface, it sounds like the conditioners would be a better choice. Not only is there no sodium, but the lack of potassium reduces the risk of overdosing on that mineral if you're also using potassium salt replacements in your food.
But that's not the only thing you need to know about water conditioners. They're not just passive systems that work no matter what. If your local tap water has a lot of contaminants, for example, the conditioner might not work as well as it would in another region where the tap water was cleaner.
Conditioners are easier to maintain and use, though, so if you're not really into doing a lot of home inspections, a water conditioner might actually be a lot better for you, even if you aren't trying to skip the salt in your diet.
Check with a few water conditioning places to see what they offer, and ask your neighbors if any of them use a conditioner. These systems work quite well for many people can provide that relief you need from small but persistent worries over salt levels.