in my 15+ years in the water treatment industry, I have been asking the same question. I have posted a couple of answers to this question on this site previously.
There are a couple of salt free "technologies" around, but the way that they claim to work is a bit different.
Magnetic softener
The first is the magnetic "softener". This has been around for over 100 years and is still hotly debated as to whether or not it actually accomplishes anything.
All of the evidence presented by the manufacturers is anecdotal with very sketchy science to back up their claims. These do not claim to remove hardness from the water, rather they claim to rearrange the molecules in the water to prevent scale from forming.
I sat through a lecture about a year ago where the presenter proved that the weak magnetic field over a short length of pipe, combined with the speed of the water moving through said field was not able to accomplish any tangible results.
- However, there have been measured results with this system as part of a larger water treatment system in some industrial settings.
- The presenter did state that there were anti-scaling chemicals in use along with the magnet, so the results were inconclusive.
Catalytic water softener
It seems that one technology that will accomplish some removal of minerals from the water is called a catalytic water softener.
This system causes the minerals to combine together into a form which will not form a scale. This is showing some promise, but the water conditions need to be very good, with no iron or anything else present, to see any sort of benefit.
As with the magnets, the water passes through the system with very little happening, but it does show slight benefit.
The holy grail of the water industry
The salt free water softener is truly the Holy Grail of the water industry. This is something that manufacturers are working toward and I am sure we will see it within the next decade.
A very early system using deionization (DI) technology is available.
For now, the only tried and true method for removing hardness from the water is an old school water softener. These machines have come a long way and are much more efficient than they were just a few years ago.
- If sodium is the concern, it is important to remember that the amount of sodium added to the water is identical to the amount of hardness removed.
- In most areas, this becomes a negligible amount.
- It is also important to remember that any water softener can also work using potassium salt as the regenerant