Showering in a thunderstorm is risky: if lightning strikes your house, it can run through the plumbing and reach you at the showerhead or the tap. The US National Weather Service advises people indoors in a storm to keep away from plumbing, including sinks, baths and taps. Cleveland Clinic says to wait at least 30 minutes after the last thunder before you shower.
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How lightning gets indoors
A strike on a house looks for the easiest route to the ground. Pipes and electrical wiring offer that route, so the current follows them through the building.
Steve Ackerman and Jonathan Martin, atmospheric scientists at the University of Wisconsin-Madison, say most indoor lightning injuries come from this kind of conduction. Many homes have metal water pipes, and lightning can travel a long way along metal. The metal does not draw the strike in, they point out. It gives the current a path once the strike has landed.
Plastic pipes do not make it safe
A common reply is that modern homes use plastic pipes. Cleveland Clinic’s emergency physician Dr Christopher Bazzoli says that does not help, because the water inside them still carries the current. When the current reaches the end of the line, he says, it can jump from the showerhead or tap to the person standing there.
The same risk applies to anything that puts you in contact with running water. Cleveland Clinic lists bathing, washing dishes and washing your hands as unsafe while a storm is overhead. Cleveland Clinic adds landline phones, since anything plugged into the wall is wired into the same paths.
There is one piece of better news. Bazzoli says a strike conducted through a home is usually far less severe than one outdoors. Indoors the current has further to travel and more ways to split up and fade.
How big is the risk?
Lightning is common, though the count depends on who you ask. The Wisconsin scientists put strikes in the United States at about 25 million a year. Cleveland Clinic gives a figure of about 40 million ground strikes a year.
Being hit is rare. Cleveland Clinic cites the US Centers for Disease Control and Prevention on the odds, at less than one in a million for a direct or indirect strike. It says 90% of strikes on people are not fatal, but a strike can still leave lifelong injuries. Lightning kills about 20 people in the United States a year, according to the Wisconsin pair, and severely injures hundreds more.
Being inside is not a full shield. Cleveland Clinic says a third of all lightning injuries happen indoors.
When to shower again
Wait at least 30 minutes after you hear the last roll of thunder. Bazzoli says the riskiest moments come just before and just after a storm. Strikes often reach 10 miles from the cloud, so if you can hear thunder you are still in range.
The Wisconsin scientists make a related point about the “bolt from the blue”. This is a strike that starts inside a cloud, travels away from it and hits the ground under a clear sky. A storm a few miles off can still reach you.
Flats, tall buildings and caravans
A large block of flats lowers the risk without removing it. Tall commercial buildings often carry lightning rods, Cleveland Clinic says. Bazzoli adds that a big building gives the current more routes to the ground. Anything on the path a strike takes can still be at risk.
A camper van or caravan with its own plumbing and wiring needs the same care as a house. A tent gives no protection at all, and Cleveland Clinic advises finding a building or a vehicle instead.
Outdoors, never shelter under a lone tree. When lightning hits a tree, the current spreads out across the ground, and this ground current causes most lightning deaths and injuries. The advice from both sources comes down to the same line: when thunder roars, go indoors.
