Baking soda does not chemically soften water, but it makes the water slicker and feel softer to the skin. Baking soda is also known as sodium bicarbonate. Washing soda, sodium carbonate, chemically softens water.
Hard water contains calcium and magnesium ions. The carbonate ions from washing soda produce a chemical reaction and remove the calcium and magnesium from the water. Water can also be commercially softened through ion exchange systems. Because soap in hard water does not lather easily, hard water creates build up in pipes and soap scum rings in bathtubs. Clothing washed in hard water wears out more quickly.