Calcium is one of two primary factors that influence the level of hardness in a given water sample. Experiment designs centered around this variable might include adding calcium to distilled water to create hard water, neutralizing the calcium in a sample of hard water by adding citric acid or battery acid, as well as comparing the effectiveness of different cleaning products, such as CLR and plain vinegar, at removing calcium buildup from a shower head that distributes hard water.
In addition to calcium, the presence of magnesium is a major component of hard water's composition. Experiment design ideas include the introduction of liquid dishwashing detergent into containers of distilled water and hard water. Hypothesize the affect of magnesium's presence on the cleansing agents in soap. After shaking both containers vigorously, observe the difference in the amount of suds formed in each. Appropriate research will show that magnesium weakens the effectiveness of cleaning agents in detergent so more soap is required; however, this necessity frequently leads to scum buildup that can be observed in homes that distribute hard water.
Sodium, when combined with other elements, can have vastly different affects on the hardness of water. Experiments to transform neutral water into hard water can be as simple as adding magnesium sulfate, more commonly known as epsom salt. Conversely, adding basic table salt, or sodium chloride, to hard water, will neutralize the magnesium and calcium components, thereby effectively softening the water without adding harsh chemicals that are dangerous for human consumption.
The temperature of hard water in a given setting will affect the buildup of magnesium and calcium in faucets and containers that hold and distribute hard water. Test a home with hard water to determine where buildup is greatest by taking samples from a showerhead, tub faucet, sink faucet, the cold and hot water lines on a washing machine and the water heater. Compare the samples to determine how temperature affects hard water.