A salt water softener is used to remove the minerals that cause water to be hard. Minerals such as sulfur, magnesium, and calcium cause limescale, which can build up on the insides of pipes and appliances, causing them to clog and reducing their efficiency. Salt water softeners are generally ion exchange systems that can work automatically or on demand.
Water is considered hard when there are more than seven grains of minerals per gallon (3.79 liters) of water. Hard water is safe to drink, and many people prefer the taste of hard water. On the other hand, it reduces the life of large and small appliances because it can coat the machinery and make it work harder. Detergents and soaps are less effective in hard water, which can leave spots on dishes and make clothing dull and stiff. Hard water and soap leave a soap scum in sinks, bathtubs, and showers. It also causes a thin film of soap to stay on skin and hair.
An ion exchange salt water softener uses sodium to remove minerals from the water. The softener consists of a matrix of resin beads, called zeolite, that are saturated with a strong brine solution. As the water passes through the beads, the minerals are trapped and sodium is released. When all of the sodium has gone out of the beads, they are washed with brine to regenerate them.
An automatic salt water softener works with a timer and washes the resin beads with brine on a regular basis, usually at night when water isn't being used. On-demand systems, also called demand-initiated systems, have a brine storage tank and regeneration occurs according to how much softened water is needed. Ordinary household salt can be used to replenish the brine for both types of systems. In some machines, salt is added directly into the tank with the resin while in others, there is a separate brine tank and the salt water is forced onto the zeolite with pressure from fresh water.
People with health conditions like high blood pressure or heart problems should not drink water conditioned by a salt water softener because of the increased sodium content. Additionally, some US cities forbid the use of salt-water softeners because of the increased amount of salt that's released in sewers and groundwater. This salt harms the environment and increases water treatment costs. As an alternative, salt-free catalytic converter softeners can be used.