Soft water

Soft water the term used to describe types of water that contain few or no calcium or magnesium metal cations. The term is usually related to "hard water", which does contain significant amounts of these ions.

Soft water usually comes from peat or igneous rock sources, such as granite but may also derive from sandstone sources, since such sedimentary rocks are usually low in calcium and magnesium.

There are water softening devices used in households and by industry to remove the hardness-causing minerals from hard water, leaving softer water. Most often, such devices exchange the calcium and magnesium ions in the hard water for sodium ions.

The main benefit of this artificially softened water is that the build-up of solid minerals (e.g. calcium carbonate) in pipe work and on heated surfaces - such as in boilers, immersion heaters or hot water cylinders - is controlled or even eliminated. However, softened water tends to be more corrosive to metals such as steel and zinc because these mineral deposits do not form and protect the corroding metal surfaces.

Water softened by sodium ion exchange will have a higher sodium ion content than the natural water it was derived from.