Drinking water supplies
It is common, in many metropolitan and urban areas, for the water supply authorities to reduce the hardness of the water from their reservoirs so that its aesthetic quality is improved from the raw water resource.  Reducing hardness is simply a matter of removing some of the calcium and magnesium ions, not all of them, just enough to make the water softer.  Since calcium and magnesium rapidly form precipitates with carbonates, adding soda ash (sodium carbonate) to water forms calcium carbonate and magnesium carbonate that then settles out as a precipitate.  Soda ash is also called 'washing soda' and its use for normal laundry purposes is to reduce the calcium and magnesium effects on soap. In detergents, phosphorus salts are used to isolate the calcium and magnesium in a different way (discussed later). Drinking water systems

In 1998,  43 town water supplies were measured across coastal and inland NSW as part of a research project.  The hardness in the water supplies was extremely variable but there were significant differences between the coastal fringe and the inland (west of the Great Dividing Range).  It is clear that inland water supplies are harder than coastal supplies. As a comparison, rainwater has a hardness of less than 5 mg/L.

Effects of hard water on soaps and detergents
The problem that hardness causes to our use of water for washing (persons and clothes) is that the calcium and magnesium salts react with the surfactant (the surface active agent) and reduce its effectiveness.  We can overcome that problem by using more washing soap to bind the calcium and magnesium. Additional amounts of washing soda (sodium carbonate) or borax can be used to precipitate the calcium and magnesium.  The problem with soaps in hard  water is that the compounds formed with the soap result in a greasy curd that is insoluble in water and difficult to wash out. It doesn't matter how much extra soap we use, the curd remains insoluble.

So if we have to learn to live with hard water, how do we overcome the effects of the hardness.  SIMPLE  - use a high quality detergent.  The harder the water, the more detergent you use.  Phosphates have been added to water to deal with hardness and these salts are very good at combining with calcium and magnesium and keeping them in suspension so that they can be effectively washed out of the clothes.  Whether substitutes for phosphorus, such as zeolites work in hard water may need to be tried.

The third way of dealing with hard water is to pass the water through a softener.

Water softeners
These devices are ion exchange systems - that is, they exchange sodium ions for calcium and magnesium ions.  Water passes through a softener. On its way through the media inside the softener, the calcium and magnesium ions are captured by the media and a replacement occurs.  Sodium ions on the media are displaced by the calcium and magnesium.  Instead of the water having say 100 mg/L (parts per million) of calcium and magnesium combined, the softened water now has very low levels of calcium and  magnesium, but levels of sodium displaced are fractionally higher than the combined calcium and magnesium displaced. At regular intervals, the ion exchanger has to be replenished, that is back flushed with a brine solution (concentrated sodium chloride solution) to replace the calcium and magnesium so the process can start again.  The backwash should be discharged to sewer and not onto the ground or into a septic tank (or other on-site system). The period between backwash events will depend upon the hardness of the water and the volume of water treated.  Check with us, for the correct sized water softener for your application.

Additional Information If you have other questions that you think the answers may help other, please email us and let us know.

References:  City West Water-Melbourne: http://www.citywestwater.com.au/about/docs/Water_Quality_Report_2007.pdf
Sydney Water: http://www.sydneywater.com.au/Publications/Reports/TypicalWaterAnalysis.pdf#Page=1
Brisbane Water: http://www.brisbane.qld.gov.au/BCCWR/LIB169/FEB2007_CHEMICAL_ANALYSIS_WATER_QUALITY_RESULTS.PDF