Electrical conductivity is the ability of any substance to conduct an electric current. For a current to flow through a liquid like water, mobile, electrically charged particles must be available. Pure water itself is an extremely poor conductor of electricity, meaning it acts more like an insulator. Distilled water, a highly purified form of water, is consequently a negligible conductor of electricity under ideal conditions.
The Role of Ions in Electrical Conduction
Water molecules are polar, but they do not readily carry an electric current across a significant distance. The flow of electricity through water depends almost entirely on the presence of dissolved ionic compounds, known as electrolytes.
When salts, minerals, or acids dissolve in water, they separate into positively and negatively charged ions. These free-moving ions, such as sodium, chloride, calcium, and magnesium, act as the charge carriers that allow electricity to travel through the liquid. The greater the concentration of these dissolved ions, the higher the water’s electrical conductivity will be. Measuring conductivity is a common method for assessing the total dissolved solids (TDS) and overall purity of a water sample.
Defining Distilled Water and Its Purity
Distilled water is produced through the process of distillation, a highly effective method for removing non-volatile impurities. The process involves boiling water to create steam, separating the pure water vapor from dissolved solids, minerals, and salts. The steam is then collected and cooled, condensing it back into a liquid state that is virtually free of the ionic impurities that conduct electricity.
The removal of conductive ions makes distilled water an extremely poor electrical conductor, with conductivity typically ranging from 0.5 to 3 microsiemens per centimeter (\(\mu\)S/cm). Theoretically perfect, ultra-pure water has an even lower conductivity of about 0.055 \(\mu\)S/cm at 25 degrees Celsius. Distilled water can absorb carbon dioxide (CO\(_2\)) from the air, which forms a trace amount of carbonic acid. This reaction introduces a minimal number of ions, causing the conductivity to increase slightly over time, but it remains a very poor conductor for practical purposes.
Comparing Distilled Water to Common Water Sources
The difference in conductivity between distilled water and common water sources is due to their ion concentrations. Tap water, fresh river water, and spring water all contain various levels of dissolved minerals, such as calcium, magnesium, and bicarbonate. This mineral content gives typical tap water a conductivity often between 50 and 800 \(\mu\)S/cm, making it hundreds of times more conductive than distilled water.
Saltwater, such as seawater, represents the high end of the conductivity spectrum because of its high concentration of dissolved sodium chloride and other salts. Seawater typically exhibits a conductivity around 50,000 \(\mu\)S/cm, making it a very efficient electrical conductor. Common water sources can be dangerous near live electrical currents, as the dissolved ions readily transmit the charge. Because of its lack of ions, distilled water is essential in applications where electrical interference or mineral deposits must be avoided, such as in scientific laboratories, medical equipment, and automotive batteries.