The idea that water is an excellent conductor of electricity is a deeply ingrained public belief, but the fundamental science is more nuanced. Pure water, specifically \(\text{H}_2\text{O}\), is actually a poor conductor of electrical current, behaving more like an electrical insulator. This is because the water molecule is covalently bonded, meaning it does not easily break apart into the free-moving charged particles necessary for electrical flow. The true danger of water lies not in the \(\text{H}_2\text{O}\) molecule itself, but in the substances it dissolves. Understanding this distinction is the first step toward appreciating why water can be so dangerous in real-world electrical scenarios.
The Science of Conductivity Pure Versus Impure Water
Electrical conductivity in any liquid requires mobile charged particles, known as ions, to carry the current. In liquids, electricity is carried by the movement of these positive and negative ions, not by electrons as in a copper wire. Highly purified water, such as distilled or deionized water, contains almost no dissolved ions, making it highly resistant to electrical flow. Ultra-pure water can have a resistivity of up to \(18.2 \text{ megaohm-centimeters}\) (\(\text{M}\Omega\text{-cm}\)) at \(25^{\circ}\text{C}\), indicating it is a very effective electrical barrier.
The challenge is that perfectly pure water is almost nonexistent outside of a laboratory setting. As soon as water touches anything—soil, pipes, air, or human skin—it begins dissolving trace amounts of minerals, salts, and gases. These dissolved solids provide the necessary ions for conduction. For instance, common table salt, sodium chloride (\(\text{NaCl}\)), immediately separates in water into positively charged sodium ions (\(\text{Na}^+\)) and negatively charged chloride ions (\(\text{Cl}^-\)).
Tap water, lake water, and especially saltwater are highly conductive because they are electrolyte solutions rich with ions. The amount of dissolved salts and minerals dictates the water’s conductivity; the more impurities present, the lower the electrical resistance. Even carbon dioxide (\(\text{CO}_2\)) from the air dissolves in water to form carbonic acid, which weakly dissociates and introduces ions that contribute to current flow. The electrical resistance of typical tap water is significantly lower than that of pure water, often by a factor of a million or more, which is why it poses a shock hazard.
When a voltage is applied, positive ions migrate toward the negative electrode, and negative ions move toward the positive electrode, collectively creating a flow of electrical current. This makes the water part of the electrical circuit, capable of transmitting charge from a source to anything submerged within it.
The Chemical Reaction Electrolysis
While simple conduction involves the passage of current through water via dissolved ions, a more intense electrical process can occur when a voltage is applied: electrolysis. This is the chemical decomposition of water (\(\text{H}_2\text{O}\)) into its elemental components, hydrogen gas (\(\text{H}_2\)) and oxygen gas (\(\text{O}_2\)), using electrical energy. This process requires an electrolyte to be present, which is why pure water must be “salted” or acidified to increase its conductivity for practical electrolysis. Electrolysis takes place within an electrolytic cell, which contains two electrodes: the anode (positive) and the cathode (negative).
At the cathode, a reduction reaction occurs where water molecules gain electrons to form hydrogen gas and hydroxide ions (\(\text{OH}^-\)). Simultaneously, at the anode, an oxidation reaction occurs where water molecules lose electrons to form oxygen gas and hydrogen ions (\(\text{H}^+\)). The overall chemical equation is \(\text{2H}_2\text{O} \rightarrow \text{2H}_2 + \text{O}_2\), demonstrating that twice the volume of hydrogen gas is produced compared to oxygen gas. This chemical decomposition is a non-spontaneous reaction, requiring a continuous external source of electrical energy to drive the splitting of the water molecule. Electrolysis is primarily used in industrial applications for the production of hydrogen fuel.
Practical Implications and Safety Hazards
The real-world danger of electrified water stems directly from its ability to conduct current due to dissolved impurities, particularly when a person is involved. Human skin, when dry, provides a high electrical resistance, sometimes over \(100,000 \text{ ohms}\), which limits current flow. However, when skin is wet or submerged in water, its resistance drops dramatically, effectively bypassing this protective layer. When submerged, the body’s total electrical resistance can decrease to as low as \(1,000 \text{ ohms}\) or even closer to the internal body resistance of about \(300 \text{ ohms}\).
This massive reduction in resistance means that even common household voltages, such as \(120 \text{ volts}\), can drive a lethal amount of current through the body. A current of \(100 \text{ milliamperes}\) (\(0.1\) ampere) is enough to cause ventricular fibrillation. A wet body exposed to \(120 \text{ volts}\) can easily experience currents several times that level.
Common scenarios like faulty underwater lighting, damaged electrical pumps, or extension cords falling into pools, hot tubs, or flooded basements can energize the water, leading to electric shock drowning. In these environments, the current spreads through the water, creating a voltage gradient, or difference in electrical potential, between two points. A swimmer who bridges this gradient becomes the path of least resistance for the current. To mitigate these risks, safety devices like Ground Fault Circuit Interrupters (GFCIs) are mandatory for outlets near water sources.
A GFCI constantly monitors the electricity flowing into a circuit versus the electricity returning and instantly cuts power if a small difference, or fault, is detected, preventing a serious shock. If someone appears to be receiving a shock in the water, the safest course of action is to immediately shut off all power to the area before attempting a rescue, and never enter the water yourself.