Water softeners are designed to remove dissolved mineral components like calcium and magnesium from water before they can separate. Hard water can stain clothes and sinks and cause scale buildup in pipes, but water softeners remove the minerals in hard water before they can cause damage. These softeners replace the minerals with sodium ions using a salt mixture. However, for those who are sensitive to sodium or do not want added sodium in their diets, there are salt-free water softener options.
Potassium chloride is a material that can be used in water softeners to create the brine needed to replace mineral ions. It works the same way salt does, and can be used in the same water softener systems, but does not add sodium to the water and does not use salt at all. Potassium chloride is more expensive than salt.
Polyphosphates are a useful family of chemicals that are not harmful to humans in low amounts, but interact with particles in hard water like iron and manganese molecules. The polyphosphates bind to these particles readily, but do not allow them to bond to other materials. As a result, the particles move through the water system without damaging pipes or sinks.
Chlorination filters use chlorine to precipitate materials like iron and manganese from the water before they can form damaging layers in the plumbing. Chlorine causes the particles to emerge from their dissolved state, where they can be easily filtered out using a common household filter that is included as part of the system. Many filters also include a carbon filter or similar device to remove the chlorine.
Greensand is a type of filtering material made of glauconite particles. Like chlorine, glauconite causes the metallic and mineral particles in water to precipitate. They are then caught in the sand itself, while the water passes through uninhibited. These filters are useful for spot applications under sinks or near major appliances, but the water pH must relatively low for the greensand to work effectively.