To extract the high mineral content of hard water, the softener runs the water through a tank of salt pellets. Traces of salt remain in the water, but how much depends on the amount of minerals in your water before treatment. Although the amount of salt in the water is negligible, if you suffer from hypertension and don't want to take chances, you can use bottled water for drinking and cooking.
Salt in the water reduces ability of soap to lather. Because of this, laundry detergents and other household soaps may not work as well or you may have to use more. Also, many people feel that salt-softened water makes it difficult to wash off soap when showering, leaving a slimy feeling.
Salt has corrosive properties that can damage appliances over time. People have reported needing to replace water heaters more often, and salt-softened water shouldn't be used in spas and pools because of possible damage to pumping equipment.
Although there is disagreement about how much salt in the water can damage plants, most experts advise caution. It's better to let salt-treated water sit overnight or give plants water that hasn't been processed through a softener. Additionally, some plant root systems may be more sensitive to salts and can be damaged.
Aquarium experts suggest not to use salt-softened water in aquariums for a variety of reasons. Not only can the level of salt in the water harm some fish, but it also can damage aquatic pants. The softer water can be beneficial for some types of fish and plants, but the presence of the salt can upset the delicate balance needed for aquariums.