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The term hard water comes from the fact that it is “hard” to make foam or suds when soap is used in hard water.  Hard water contains ions such as Ca²⁺, Mg²⁺, or Fe²⁺ that react with ordinary soap to form “scum,” an insoluble sticky residue.  Scum is the “ring around the bathtub” that has to be scrubbed away with Comet or some other abrasive household cleaner.  Hard water thus causes you to use more soap than necessary just to get a little bit of suds.  This wastes the soap and costs you money.  Additionally, when hard water is heated to boiling, the ions above (especially Ca²⁺) form a scale most commonly CaCO₃ on the pipes in which the water flows or in the hot water heater.  This scale builds up over time clogging the pipes and eventually requiring replacement.  This is another expense caused by hard water.

In order to “soften” hard water you have to remove the ions.  There are several ways to do this.  A modern process called “ion-exchange” can be used in which Na⁺ ions are substituted for the more harmful ones.  Distilling water removes all ions as well, and thus we can use distilled water as a standard for comparison during today’s experiment.

This experiment is designed to allow you to test water from several sources for “hardness” and to learn several processes by which to “soften” the water you test.