The common understanding that water and electricity are a hazardous combination stems from fundamental physics principles. While pure water itself is an electrical insulator, the water encountered in daily life is far from pure. This combination creates a scenario where the human body can become an unintended pathway for electrical current, leading to severe injury or death. Understanding the mechanics of this danger is important for promoting electrical safety.
The Role of Impurities in Electrical Conductivity
The danger begins with a nuance in physics: truly pure water is a poor conductor of electricity. Water molecules (H2O) do not efficiently carry an electrical current on their own. If electrodes were submerged in perfectly distilled or deionized water, very little current would flow.
The water people encounter every day, such as tap water, pool water, or even rainwater, contains dissolved impurities. These impurities include minerals, salts, and various chemical compounds that break down into charged particles called ions. Common examples are positively charged ions like calcium and sodium, and negatively charged ions like chloride and sulfate.
These free-floating ions act as the carriers for electrical current. They migrate toward the oppositely charged source, effectively lowering the water’s electrical resistance and allowing current to flow readily. Tap water, for example, can have a conductivity range vastly higher than distilled water due to these dissolved solids.
When a person stands in or touches a body of conductive water that is in contact with an energized source, the water drastically lowers the resistance of the overall electrical path. This lowered resistance means that according to Ohm’s Law (Current = Voltage / Resistance), a dangerously high amount of electrical current can pass through the body. The moist skin and the water bypass the body’s natural primary defense, which is the high resistance of dry skin.
How Electric Current Harms the Human Body
Once an electrical current enters the body, the harm is caused by three primary mechanisms: disruption of bioelectrical signals, cardiac electrocution, and thermal burns. The severity of the injury depends on the current strength, the duration of exposure, and the path the current takes through the body.
The human nervous system and muscles operate using minute electrical impulses, and an external current can completely override these signals. When a strong alternating current (AC) passes through muscle tissue, it can cause tetanic contractions, which are sustained, involuntary muscle spasms. If the current causes the flexor muscles of the hand to contract, a person may be unable to let go of the energized source, prolonging the exposure.
A current passing across the chest cavity is particularly dangerous because it can disrupt the heart’s rhythm. Currents as low as 50 to 120 milliamperes (mA) can induce ventricular fibrillation. This is a chaotic, ineffective quivering of the heart’s lower chambers, which prevents the heart from pumping blood and rapidly leads to cardiac arrest and death.
The third damaging mechanism is the generation of heat as the current passes through tissues. Tissues with higher resistance, like bone and skin, convert more electrical energy into heat. This causes severe internal and external thermal injuries, which are often concentrated at the entry and exit points on the body.
These electrical burns can cause deep tissue destruction, damaging nerves and blood vessels in the current’s path. The damage can extend far beneath the skin, causing extensive necrosis that is not immediately visible on the surface.
Essential Safety Devices for Wet Environments
Engineering solutions are in place to mitigate the risks posed by electricity in damp or wet locations. Grounding is a foundational safety measure that provides a low-resistance path for fault current to return to the earth or the source, bypassing the human body. This is accomplished through the dedicated ground wire, typically the third prong on a plug, which ensures that if a fault occurs, the current trips the circuit breaker rather than using a person as a conductor.
The ground fault circuit interrupter (GFCI) offers a specialized level of protection against electrocution hazards. This device constantly monitors the current balance between the hot and neutral wires in a circuit. In a normal circuit, the current flowing out should precisely match the current flowing back.
If a current “leaks” out of the circuit—for instance, through water and then a person—a ground fault occurs, creating an imbalance. The GFCI is designed to detect a difference as small as 5 milliamperes and instantly trip the circuit, shutting off the power in as little as 1/40th of a second. This rapid response time is fast enough to prevent the lethal effects of an electrical shock, making GFCIs indispensable in bathrooms, kitchens, and outdoor areas where water is present.