There is a set of devices that claim to treat hard water and make it behave like soft water. These are known as hard water conditioners. They basically use a magnetic field to treat the hard water.
Water conditioners use a magnetic field to charge the minerals and water molecules and prevent the minerals from acting "hard". This means that the calcium and magnesium minerals will not deposit and form scale, and they will not interfere with soap. And charged water molecules end up with a lower surface tension and the ability to dilute more minerals. The combined effect is that there is no scale formation and water feels a bit softer because of the lower surface tension. It is important to note that the chemistry of the water will not change, so the calcium and magnesium will remain in the water. They simply will be rendered harmless for a period of time and the water will behave as softened water.
So that's all great on paper. The physics makes sense, but that doesn't mean that the devices out there in the market work.
There are 2 types of water softeners (or rather conditioners) that use magnetic fields. There are those that are magnetic, and those that are electronic. Magnetic field water softening (or conditioning) is scientifically proven to work. But the problem is that it requires a really strong magnetic field which most devices are not able to create. So you have lots of magnets and electronic gadgets out there taking advantage of the scientific research, but only for marketing purposes because they usually don't work well because they do not create a magnetic field that is strong enough to affect the water molecules. I should know because I tried a few of them. Of course, there are always exceptions. Out of the ones I tried, I found a magnetic brand that works, but none of the electronic ones I tried worked for me. If you are planning on trying a specific brand, make sure you know someone who used it before so you can get an idea of its effectiveness.
One thing that most manufacturers of water conditioners don't tell you is that the effects of the treatment last for a certain period of time. So the water passes through the magnetic field and it gets charged, right? Well this lasts for around 2 days, which is more than enough for that water to travel through your home pipes and out of the faucet. But an important consideration is the water heater. Water sits there for a while. In addition to that, the heating probably dirupts the effects of the magnetic field. So the water coming out of your water heater may not be "soft" anymore, and it will still damage your shower head and water pipes and appliances. Some magnetic brands give you two magnets, one for the water coming in to the house, and the other for treating the hot water coming out of your water heater. None of the electronic devices I researched or tried offered 2 units, so if you opt for that, you will have to buy 2 of them.
The biggest advantage is that they are much cheaper than regular water softeners. Also, a magnetic or electronic water conditioner that works has many advantages over your regular water softener like:
They also have disadvantages of course:
If you know of a good brand, go for it. A magnetic one I bought worked wonderfully for me.