Although many people think water conducts electricity well, pure water is a poor conductor since its molecules do not have free electrons to travel and thus transfer current. Pure water, however, rarely exists in nature. Salts, sediments and minerals often mix with water and create ions that conduct electricity.
Water exists virtually everywhere and dissolves a variety of minerals, such as calcium, magnesium and salts. These substances are ions, or atoms that have a net electrical charge. When electrons are introduced into ionized water, they can transfer from one ion to the next, creating an electrical current through the water. The more minerals that are dissolved in the water, the more efficiently it will conduct electricity.
Even completely pure water will carry a current in the presence of enough voltage, such as in the case of a direct lightning strike. There is no such thing as a perfect insulator by current human knowledge.
Pure water consists of one oxygen molecule chemically bonded to two hydrogen molecules. Oxygen has eight electrons, with two in its inner shell and six in its outer reactive shell. The outer shell has room for
eight electrons. Because hydrogen atoms have one electron each, a perfect chemical bond forms.