An electric current is created when electric charges move through a material. In metals this movement is carried by electrons. In liquids such as water the charge is carried by ions.

Pure water consists of neutral H2O molecules. These molecules do not carry a full electrical charge that could move freely through the liquid. For this reason pure water is a very poor conductor of electricity.

For electricity to flow through water there must be charged particles present. These particles are called ions. Ions form when atoms or molecules gain or lose electrons and therefore become electrically charged.

When ions are dissolved in water they can move through the liquid. If an electrical voltage is applied positive ions move toward the negative electrode and negative ions move toward the positive electrode. This movement of charged particles creates an electric current.

In everyday life water usually contains dissolved substances from minerals and salts. As water moves through soil and rocks it dissolves small amounts of these materials. This process introduces ions such as calcium sodium magnesium and chloride into the water.

Because of these ions tap water conducts electricity much better than pure water. Distilled water contains almost no dissolved ions and therefore conducts electricity very poorly.