Water softeners: How much sodium do they add?

The amount of sodium a water softener adds to tap water depends on the "hardness" of the water. The best way to decrease your sodium intake is by cutting back on table salt and processed foods. But the water from your tap also may add a significant amount of sodium to your diet. Reducing dietary sodium can lower systolic blood pressure by 2 to 8 millimeters of mercury (mm Hg).

Hard water contains large amounts of calcium and magnesium — dissolved from the soil by rainwater. A typical water-softening system removes calcium and magnesium ions from hard water and replaces them with sodium ions. The higher the concentration of these minerals, the more sodium needed to soften the water.

Contact your local health department for the sodium and other mineral content of your community's water supply. Water naturally contains some sodium. This information can help you determine the total amount of sodium your tap water may have before being softened.

It can also help you estimate the amount of sodium (milligrams per liter) a softener adds to your water. Use the following formula:

• Multiply the hardness of the water in grains per gallon by 8 (or 7.866 to be more precise).
• Add this figure to the amount of naturally occurring sodium in your water (the figure you get from the local health department) to determine total sodium.

If you find that your tap water is high in sodium, you may consider:

• Switching to another type of water-purification system
• Buying demineralized water for drinking and cooking
• Softening only the hot water and using unsoftened cold water for drinking and cooking