Being in water during a thunderstorm presents an extreme and often fatal hazard. Lightning is a massive, rapid electrical discharge that seeks the path of least resistance to the ground. This powerful, high-voltage current makes contact with water during a storm exceptionally risky. Immediate action is necessary upon the first sign of a storm to prevent serious injury or death.
Why Water Is Dangerous During a Storm
The danger of water during a storm stems from its electrical conductivity, which is driven by dissolved materials. While pure water is a poor conductor, natural water sources like lakes, pools, and oceans contain high concentrations of dissolved salts, minerals, and impurities. These create free-moving ions, known as electrolytes, which allow the water to become an effective pathway for the electrical energy of a lightning strike.
When lightning strikes the surface of water, the electrical current does not dissipate harmlessly throughout the entire volume. Instead, the energy spreads rapidly across the surface in all directions from the point of impact. This radial dispersal creates a lethal zone called “surface current.” The highest concentration of electrical energy remains confined to a shallow layer near the surface, posing a direct threat to anyone swimming or standing in the water.
The current strength declines exponentially as it moves outward, but a significant electrical potential can extend for tens of meters. The jolt can remain dangerous enough to cause cardiac arrest, severe burns, or muscle paralysis up to 20 to 30 meters from the strike. Water acts as a massive conductor, instantly transforming a wide surface area into a deadly electrical field, making an indirect strike almost as dangerous as a direct one.
Risk Levels for Different Water Environments
The specific environment dictates the severity and nature of the lightning risk, as surrounding infrastructure can introduce new conductive pathways. In open water environments, such as oceans, lakes, or rivers, the danger is primarily from the lack of a higher, grounded structure nearby to absorb the strike. Swimmers or people in boats often become the tallest objects, increasing the likelihood of a direct strike. Even if the strike misses the person, the surface current spreads across the vast expanse of water, leaving no safe area to escape.
Swimming pools, whether outdoors or indoors, carry a unique set of risks due to their interconnected metal components. Lightning does not need to strike the water directly to pose a threat, as a nearby strike can energize metal objects like fences, ladders, diving boards, or filtration systems. These metal pathways, which are often connected to the pool’s water through plumbing, efficiently conduct the electricity into the pool water itself. Even an indoor pool is not immune, as the building’s wiring and plumbing can carry a charge into the facility.
A different, yet equally serious, concern exists for water connected to a structure’s plumbing system. Using indoor plumbing during a storm, such as taking a shower, washing dishes, or doing laundry, can be hazardous because lightning can travel through the metal pipes and the water inside them. While modern homes may use plastic pipes, the water itself and any connected metal fixtures still provide a conductive path for a powerful electrical surge. It is best to avoid all contact with running water and plumbing fixtures until the storm has safely passed.
Immediate Action and Seeking Safe Shelter
The moment thunder is heard, regardless of whether rain has started or lightning has been seen, is the time to immediately seek shelter. A reliable guideline for determining the proximity of a storm is the “30/30 Rule.” This rule states that if the time between seeing the flash of lightning and hearing the thunder is 30 seconds or less, the storm is close enough to pose a significant danger, and shelter must be sought at once.
The first part of the rule is based on the calculation that sound travels approximately one mile every five seconds, meaning a 30-second count indicates the storm is within about six miles. A safe shelter is defined as a substantial, fully enclosed building with complete wiring and plumbing to direct electrical current safely to the ground. If a secure building is unavailable, a fully enclosed metal vehicle, such as a car or truck with the windows rolled up, offers the next best protection because the metal frame acts as a protective cage.
Once a safe location is reached, the second part of the rule dictates that activities should not resume until 30 minutes after the last sound of thunder is heard. This waiting period is necessary because lightning often strikes well before or after the main part of the storm passes, and can occur up to 10 miles away from the rain. Unsafe places to shelter include small, open-sided structures, under tall or isolated trees, and on porches or balconies.