Does Adding Salt to Water Make the Water Softer & PH Lower?

Hard water can cause scale buildup in places like your bathroom.

Hard water contains high levels of calcium and/or magnesium ions. These ions can form insoluble compounds like calcium carbonate and leave stains called scales on faucets, pipes or other surfaces. Some water softeners use ion exchange systems that swap sodium for calcium or magnesium ions, increasing the sodium content of the water. Adding sodium chloride to water by itself, however, will not make the water softer, nor will it have any effect on pH.

Solubility

Magnesium chloride and calcium chloride are both soluble salts. Consequently, adding sodium chloride to water will not cause the magnesium or calcium to precipitate. Moreover, sodium chloride will have little effect on the solubility of calcium carbonate or other insoluble calcium compounds. Addition of large quantities of salt reduces the number of water molecules available to interact with calcium or carbonate ions, so adding a large quantity of salt could decrease the solubility of calcium carbonate, but this is neither practical nor would it achieve the desired goal -- removing calcium and magnesium from the water.

Effect on pH

Sodium chloride is a neutral salt produced by a reaction between a strong acid called hydrochloric acid and a strong base called sodium hydroxide. It has no effect on the pH of the solution, because the chloride ion is the conjugate base of a strong acid, so chloride ion is an extremely poor base. Adding sodium chloride will not reduce the pH of your water to any measurable extent.

Ion-Exchange Systems

An ion exchange water softener uses cation exchangers, negatively charged groups that are initially coated with positively charged sodium ions. When water containing calcium or magnesium ions flows through, the calcium and magnesium ions have a higher affinity for these negatively charged groups than the sodium ions, so they take the place of the sodium ions. The net result is decreased water hardness, although this type of system does increase the sodium content of your water.

Considerations

If you're having problems with water hardness, an ion exchanger is one option you can consider, although increased sodium content may not be suitable if anyone in your family has a health problem that requires them to limit their sodium intake. Some water softeners can use potassium ions instead. One thing is for certain, however: just adding salt to your water won't really affect its hardness or pH. It will just make the water saltier, which could even make it unsuitable to drink.

References

• North Dakota State University, Treatment Systems for Household Water Supplies: Softening
• Texas A&M University Ag Facts: Hard Water
• Lenntech: Water Softener FAQ