Water is the most important molecule that exists on the Earth. Without water living beings would not be able to live. Water is used for an immeasurable number of things. There are many properties of water, which makes this molecule so unique. One which people overlook is hardness. Hardness is defined in the Chemistry: The Central Science by Prentice Hall's as being "water that contains a relatively high concentration of Ca2+, Mg2+, and other divalent cations." Water containing these ions is not a health hazard; however, it is a problem for industries and households. Therefore, the hardness of water is vital to understand in order to prevent the problems it could cause. For one to have a better understanding of hardness, you must know how water becomes hard or what causes water to become hard. All water that we use is freshwater which is transported through many pipes. The ions Ca2+ and Mg2+ react with water and form insoluble substances which causes blockage and deposits to form. Some examples of how this affects industries and households are the insoluble substances that form and cause soap scum, scaling in water heaters in factories, and clogging of pipes which transports water places. There are many techniques in which water undergoes in order to decrease the amount of ions in the water before the water comes to your faucet. Although people can take most ions out of the water, not all ions can be removed. The following chart shows the classifications of water and their hardness. In this chart, 1 ppm hardness is equal to 1 part of CaCO3 per million parts water, which is also equal to 1 mg CaCO3 in 1 liter of water. Table A Concentration mg/L CaCO3 Description 0 - 75 soft 75 - 150 moderately hard 150 - 300 hard 300 and up very hard This data is used as a guideline for people to determine how hard/soft the water is. An experimental procedure in Penn State's version of Chemtrek August 2000-July 2001 on pages 10-12 to 10-20, which was written by Stephen Thompson, is a good procedure to determine the hardness of water.