The question of whether water softened with salt is safe to drink often stems from a misunderstanding of the softening process. Generally, softened water is safe for most people to drink, but the sodium added during the process requires attention. Water softening removes high concentrations of “hard” minerals, primarily calcium and magnesium, which cause scale buildup in plumbing and appliances. These minerals are successfully removed and replaced with a small, measurable amount of sodium, which is the source of public concern.
How Ion Exchange Softeners Work
A salt-based water softener uses ion exchange, a chemical process that removes positively charged hard minerals. Inside the softener tank are thousands of small resin beads coated with positively charged sodium ions. As hard water flows through the resin bed, the calcium and magnesium ions, which have a stronger positive charge, are attracted to the beads.
The resin beads capture the calcium and magnesium ions, releasing the less-strongly held sodium ions into the water. This exchange continues until the resin beads become saturated with hardness minerals. The “salt” added to the softener is sodium chloride (or sometimes potassium chloride), used in a concentrated brine solution to regenerate the beads and flush the accumulated minerals down the drain. The resulting softened water contains a small amount of sodium, which is a byproduct of the ion exchange.
Calculating the Added Sodium Content
The amount of sodium added is directly proportional to the initial hardness of the water being treated. The harder the incoming water, the more sodium is released into the softened water. For every one grain per gallon (gpg) of water hardness removed, approximately 7.9 milligrams per liter (mg/L) of sodium is added.
If water has a moderate hardness of 10 gpg, the softening process adds about 79 mg of sodium per liter. An eight-ounce glass contains around 19 mg of sodium. This is a very low amount compared to a single slice of whole wheat bread (over 200 mg) or an eight-ounce glass of milk (about 125 mg). For most people, the increase in sodium from softened water is negligible compared to a typical diet.
Health Implications of Increased Sodium Intake
For the general population, the small increase in sodium from drinking softened water poses no health risk. The amount added is minimal and contributes an insignificant percentage to the recommended daily intake. Even water with a high hardness level (20 gpg) adds less than 40 mg of sodium to an eight-ounce glass, meeting the FDA’s definition of “very low sodium.”
The sodium content becomes a serious consideration for individuals on a doctor-ordered, extremely low-sodium diet, such as those with heart or kidney conditions. For these sensitive populations, sodium intake must be carefully monitored. Infants, especially when formula is mixed with softened water, are another group where increased sodium should be considered.
In these cases, a medical professional should be consulted. A common solution is to install a bypass line during softener installation so the main drinking water tap is supplied with unsoftened water. Alternatively, a separate point-of-use filter can be installed on the drinking water tap to remove the sodium.
Low-Sodium Softening Alternatives
For those who need soft water but must avoid the sodium increase, alternatives to the standard sodium chloride system exist. The primary low-sodium option is using potassium chloride (KCl) instead of sodium chloride salt in the ion exchange unit. Potassium chloride works the same way, exchanging potassium ions for the hardness minerals.
This alternative is appealing to those on sodium-restricted diets because potassium is an essential nutrient. While effective, potassium chloride is typically more expensive than sodium chloride and may require a slightly larger quantity for the same softening level. Another option for removing sodium from drinking water is installing a reverse osmosis (RO) system at the point of use. An RO system removes virtually all dissolved solids, including the sodium added by the water softener.