Ionic substances conduct electricity when they are dissolved in water. Ionic substances release ions into water so that they carry electricity through the solution. Water containing dissolved ions is a very good conductor of electricity.
The freely moving ions in the water have the ability to pass electricity through the solution. Covalent substances cannot conduct electricity when they are dissolved in water, as they are not then able to produce ions. Pure water by itself is also not a good conductor of electricity unless it is mixed with any ionic compound. The solution that can conduct electricity is called an electrolyte, and that which cannot conduct electricity is called a non-electrolyte.