The removal of hardness with an ion exchange water softener does not affect the factors, which cause or accelerate corrosion. Softening does not change the pH or carbon dioxide concentration, the dissolved oxygen concentration, or the total chemical concentration of minerals. A softener may reduce the amounts of solid particles in the water, but obviously cannot change other physical factors such as temperature, flow rates through pipes, or volumes of water used. Thus ion exchange softening neither causes nor controls corrosion. Unfortunately, certain methods of calculating the probable corrosive potential of natural waters have been misapplied to softened waters, with misleading results. The Langelier Index, and some of its modifications, may be used to indicate whether or not a particular water will precipitate calcium carbonate scale at a given temperature. This information certainly is useful to those responsible for operating many systems.

Water Quality Answers Is softened water more corrosive? No. Because the Langlier (calcium saturation) Index is lowered in water that has had calcium removed, skeptics sometimes consider softened water to be more corrosive. But softening of water via cation exchange does not make water more corrosive. In fact, the U.S. Environmental Protection Agency (USEPA) and the American Water Works Association have both recently corrected their enclosed brochures as to the misconception that ion exchange softening has an effect on the corrosivity of water.