Water molecules are composed of one oxygen molecule covalently bonded to two hydrogen molecules. In a covalent bond, the electrons are shared between two atoms, binding them to the molecule.This decreases conductivity, as a current requires electrons to travel through. Pure water, therefore, has an extremely low conductivity. The presence of impurities, such as minerals, increases the conductivity of water, as these impurities are able to ionize, or dissociate, into charged ions, creating a medium for the electricity to flow.
As the temperature of water increases, the electrons exhibit greater movement within the molecules. This increases the ability of electricity to flow more freely through the medium, establishing a higher conductivity. Water that is above or below boiling and freezing points is not a good conductor due to the rigid molecular structure of ice and the absence of ions in steam, which evaporate as pure water.
Salinity is a term used to describe the salt concentration of water. Salts are composed of ionic bonds between a positively charged atom, called a "cation" and negatively charged atom, or "anion." The addition of a salt to water results in ionization, or separation, of the ions in the water. Electricity is then able to flow through the charged ions in the water, increasing conductivity.
The strength of an acid or base is directly related to the number of free hydrogen and hydroxide ions produced in a solution. At a pH of 7, water is neutral and has no free hydrogen or hydroxide ions to conduct electricity. A subsequent increase or decrease in pH results in an increased amount of free hydroxide and hydrogen ions. As water either increases and decreases in pH from 7, it becomes a better conductor of electricity.