In a Nutshell
Is water a good electrical conductor? Most of us would say yes, but the answer is not so straightforward. Standing in it while in contact with electricity is not a good idea, but the truth is that this is not due to the water, but more so what is in it. Pure water is actually an insulator, but if we add impurities, it starts to become a conductor because certain impurities called electrolytes separate into positive and negative ions when dissolved. It is these ions that carry the current and complete an electrical circuit, which can be deadly if your body is in contact with the water and thus becomes part of that circuit.
The Whole Bushel
Common sense tells us that you should not work with a potentially live electrical wire or even plug in an appliance while standing barefoot in a puddle of water or even if your hands are wet. Most of us believe this is because water is a good conductor of electricity. Therefore, if we stand in it while handling a potentially live wire or malfunctioning electrical appliance, the water would improve the conductivity of your body and effectively complete an electrical circuit through your body to ground, causing the current to flow through you, which could result in electrocution or at a minimum, an electric shock.
The truth is that pure, distilled water does not conduct electricity at all because there is nothing in it to carry the current, but since it is an excellent solvent, it will always contain some concentration of charged particles wherever it is found in nature. Therefore, tap water always has enough impurities in it, including minerals and chlorine, to enable it to conduct electricity enough to be dangerous around electricity. What makes water more dangerous is that it will fill all open gaps between your body and any energized wires or objects so that a circuit can be completed even with just a small amount of tap water on your body. In addition, any salts from sweat on your hands will also dissolve into the water, increasing its conductivity. Impurities that can dissolve in water and conduct electricity include acids, bases, and salts. These substances are known as electrolytes, further classified as either weak or strong, which describes their relative electrolytic strength.
Vehicle batteries have an electrolytic solution of sulfuric acid (H2SO4) and water in each cell, which facilitates the flow of electricity. Newer batteries contain potassium hydroxide (KOH) or a similar alkaline hydroxide. Electrolytes promote the movement of ions from the cathode to the anode when the battery is charging and from the anode to the cathode while discharging or powering an electrical circuit. When electrolytes are dissolved in water, they separate into free moving charged particles called ions that can carry an electrical current through the water due to their mobility within the solution.
The above concept can be demonstrated with a simple experiment. Create an electrical circuit with a battery and a light bulb, interconnected with wires. Now open the circuit and put the two wire ends from the open circuit in a glass of pure distilled water. You will notice that the light bulb will not illuminate. Now, slowly dissolve some ordinary table salt in the water and the light bulb will start to illuminate and it will get brighter as more salt is dissolved in the water. This is because as the table salt, Sodium Chloride (NaCl) dissolves, the positive sodium (Na) and negative Chloride (Cl) ions separate in the water forming an electrolyte, which conducts electricity because it can carry electrons through the water. If we repeat the experiment with tap water, the bulb will illuminate before we add any salt due to some electrolytic contaminants that we will always find dissolved in tap water or any water found in nature.
Show me the Proof
How does water conduct electricity? [Link]
Water Cycle – Oceans (4) Lab [Link]
Making Electricity From Salt Water [Link]