Regular tap water contains very little sodium. The amount of sodium a water softener adds to tap water depends on the "hardness" of the water. Hard water contains large amounts of calcium and magnesium. Some water-softening systems replace calcium and magnesium ions with sodium ions. The higher the concentration of calcium and magnesium, the more sodium needed to soften the water. Even so, the added sodium doesn't add up to much.
An 8-ounce (237-milliliter) glass of softened water generally contains less than 12.5 milligrams of sodium, which is well within the Food and Drug Administration's definition of "very low sodium." Thus, it's unlikely that sodium in softened water would pose a risk for most healthy people.
A water softener will remove some iron. If the iron content is below 3 ppm, a softener will effectively remove it. Above that, your water softener will not perform a efficiently. At that point, it is advisable to consider installing an iron unit.