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Case Study: Hard Water

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    Figure 2. Depiction of Reverse Osmosis.

    Practice Problems

    1. Name the two main types of hard water. (Highlight blue area for the answers)

    Temporary and Permanent.

    2. What makes "hard" water hard?

    The presence of high concentrations of minerals, typically in the form of metal cations.

    3. What are the two most prevalent ions in hard water? How are these important to the proper function of the body?

    Calcium (Ca2+) and magnesium (Mg2+) ion. They are important because both are essential nutrients, which means they are necessary for the proper function of the body and are also important for the prevention of many diseases and other ailments.

    4. Name the four described processes for softening hard water. It is also important to understand the essential steps of each process.

    Ion exchange, chelation, lime softening, and reverse osmosis

    5. What is a major disadvantage of ion exchange when Na+ is used as a counterion?

    It increases the concentration of sodium in the water, a potential hazard for people with sodium-restricted diets.


    1. Calcium and Magnesium in Drinking Water: public health significance. Geneva, Switzerland: WHO press. 2009.
    2. Health Effects of Drinking Water Treatment Technologies. Chelsea, MI: Lewis Publishers. 1989.
    3. Lewis Alan, Scott. Safe Drinking Water. San Francisco, CA: Scott Alan Lewis. 1996.
    4. Crawford, T. and M. Crawford (1967). "Prevalence and pathological changes of ischaemic heart-disease in a hard-water and in a soft-water area." The Lancet 289(7484): 229-232.
    5. Stitt, F., D. Clayton, et al. (1973). "Clinical and biochemical indicators of cardiovascular disease among men living in hard and soft water areas." The Lancet 301(7795): 122-126.
    6. Gardiner, J. (1976). "Complexation of trace metals by ethylenediaminetetraacetic acid (EDTA) in natural waters." Water Research 10(6): 507-514.


    • Andrea Kubisch, Courtney Korff (UCD)