Electrical Conductivity

• Electrical conductivity is defined as a measure of the ease of flow of electric current. Two types of particles pass on electric current: free electrons and ions. Free electrons are found in metals, while ions are commonly found in solutions. When a dissolved substance produces ions, the solution conducts electricity and is therefore called an electrolyte. Greater ion concentration correlates with greater conductivity.
  
  

Most Common Forms of Water

• Most water that we encounter daily--for example, tap water or river water--is not pure. Such water has various dissolved substances, some of which ionize and thus increase the conductivity of water. In addition, when water is exposed to air, some carbon dioxide dissolves. To remove such impurities, water must undergo an extensive purification process.
  
  

Auto-Ionization of Water

• Even so, it is not possible to remove all impurities; therefore, to explain the conductivity of pure water, we must rely on scientific theory rather than empirical observation. Theoretically, even completely pure water would conduct electricity because of auto-ionization. Even in the absence of impurities, water would auto-ionize, or spontaneously split into a hydronium ion and a hydroxide ion. However, only 1 out of every 10 raised to the 14th power water molecules would split to yield these ions, producing a very low ion concentration.
  
  

Conductivity of Pure Water

• Because of the miniscule ion concentration in pure water, pure water has a small--but existent--electrical conductivity. This theoretical conductivity comes out to 0.0548 microsiemens per centimeter (the siemens per meter is the standard unit of measurement for electrical conductivity). The electrical conductivity value for the deionized, “ultrapure” water manufactured for scientific purposes is 0.06 microsiemens per centimeter.
  
  

Applications

• We can use electrical conductivity values for water to solve various practical problems. For one, you can use the conductivity value of pure water to determine the concentration of pollutants in rain, such as those found in acid rain. Such measurements could catalyze efforts to reduce industrial emissions. Another application is determining the viability of water purifiers by comparing the conductivity of a water sample before and after it goes through the purifier.