Why Swimming Pools Close When It Rains (Solved!)


If you’re a frequent visitor of public swimming pools, you’ve likely been unfortunate enough to experience a pool closure due to heavy rains. You would think that tiny water droplets would do no harm, so what gives? Is there a universal reason why swimming pools close when it rains?

Swimming pools close when it rains because:

  • the potential for lightning threatens swimmers’ safety
  • wet, slippery ground surfaces are a safety hazard
  • cooling effects of rain may result in hypothermia
  • rain runoff can pollute the pool
  • accompanying winds can fling natural debris and pool equipment

We will discuss these same safety hazards associated with the presence of rain in greater detail below. We’ll then discuss related topics, such as whether all pools adhere to the same rain policy and how quickly a pool can be re-opened after a downpour.

Reason #1: The Potential for Lightning Threatens Swimmers’ Safety

The most prominent reason why pool closures typically follow the onset of rain is the increased risk for lightning strikes.

What’s so scary about the prospect of lightning is that it’s tough to pinpoint precisely when and where it will strike. This unpredictable behavior makes lightning one of the more dangerous types of weather to face.

The only visual telltale sign that lifeguards have at their disposal is the presence of a rainstorm. If lightning does strike, it’s often accompanied by rain precipitation. That said, however, there have been uncommon instances where lightning has actually preceded precipitation.

Plus, lightning can actually strike outside the radius of its parent thunderstorm.

Reportedly, lightning has struck as far as 50 miles away from its parent thunderstorm. Fortunately for us swimmers, this is a fairly rare occasion.

(source)

Due to this unpredictability, a steady rainstorm can be enough for lifeguards to justify pulling the plug on pool availability. They do this to ensure the safety of all the swimmers, as the risk versus reward is not worth it under most circumstances.

Even indoor pools are not exempt from the dangers of a potential lightning strike. Lightning is known to take the past of least resistance, leading it down to unexpected locations, including metal components within indoor swimming pool facilities.

Fortunately, specific mandatory regulations are enforced to allow the electrical surge of a lightning strike to exit a swimming facility safely should this occur. These mandatory regulations are based around the following (source):

  • Bonding the Facility – Connecting all metal components into a carefully planned out, systematic grid.
  • Grounding the Facility – Providing electrical surges that find their way into the grid with a safe route out of the facility confines.

Evacuating the indoor pool when lightning has been sighted is merely an added precaution to promote swimmer safety, so don’t panic if you’re inside the building when the threat of lightning arrives.

Reason #2: Wet, Slippery Ground Surfaces are a Safety Hazard

Another reason why rain showers can cause pool closure is the slickness of the pool deck.

People are already at an increased risk of falling around pools due to water splashing onto the adjacent grounds. With heavy rains, this problem is only exacerbated.

If you do fall on the pool deck, the fall will be unforgiving. Pool decks are constructed from several hard surface materials, including (source):

  • concrete
  • wood
  • composite wood
  • stone

These deck materials may not be as slippery as your wet bathroom tile, but they can lose enough traction to cause you to take a tumble. If you hit your head and lose consciousness, the threat of drowning is also a real possibility.

In fact, there was an average of 3,536 unintentional drowning fatalities per year from 2005 to 2014. These fatalities were unrelated to boating incidents, yet this statistic still translated into approximately ten deaths per day during this timeframe (source).

So although a slick pool deck may not seem like it poses a serious problem, it’s simply not worth it for lifeguards to put swimmers at further drowning risk. From the perspective of the lifeguards, it’s better to wait for the rain shower to pass and let the pool deck dry up than to allow people to saunter around the pool deck and risk getting hurt at the expense of one dip in the pool.

Reason #3: Cooling Effects of Rain May Result in Hypothermia

Furthermore, heavy rain showers can lower a swimmer’s body temperature so severely that it results in hypothermia.

As a quick reference, hypothermia is a medical situation where the body loses heat at a faster rate than it can produce heat. This causes body temperature to drop to dangerously low levels (<95°F or <35°C), resulting in organ shutdown (source). Such dire consequences can be lethal if nothing is done to counteract these hypothermic effects.

If the pool water is already chilled to colder temperatures, the added cooling effect of the rain can make enough of a difference that hypothermic symptoms result.

To make matters worse, swimmers may mistake their hypothermic symptoms as the sudden chill that’s first experienced when immersing oneself into a pool. Consequently, swimmers continue to bask in the pool and the rain, completely unaware that the hypothermia is slowly beginning to set in.

Put simply, cold pool water combined with cold rainwater can be a recipe for disaster. This is why it’s advised that you swim in fair temperatures whenever possible. Under warmer weather conditions, the risk of hypothermia dwindles significantly.

Reason #4: Rain Runoff Can Pollute the Pool

Another potential reason why pools close when the rain comes is pool contamination. As rain runoff collects on the pool deck, it can start to filter into the pool, carrying any outdoor contaminants along with it. These contaminants can pose a health risk to any swimmer that decides to brave the effects of the rain.

You might be asking yourself, “What contaminants can rain runoff bring?” Examples of contaminants that find themselves in pool water during a rain shower include (source):

  • soil
  • mulch
  • leaves
  • dust
  • pollen
  • algae spores

If a substantial number of these contaminants gather in the pool, the precisely calculated chemical concentrations of the pool can be thrown out of balance.

For example, a high degree of soil and mulch can introduce organic contaminants into the pool, such as phosphate and nitrate. These organic contaminants make pool water an ideal setting for algae growth. With exposure to considerable amounts of algae, there’s a strong likelihood for skin infections to result (source).

In addition to organic contaminants, rainwater also affects the specific chemical gradients of the following (source):

  • pH levels
  • alkaline levels
  • calcium hardness
  • pool conditioner
  • chlorine levels

Even though such imbalances are nearly impossible to detect with the naked eye, they could result in unanticipated adverse health effects. Obviously, this is a complication that both swimmers and lifeguards wish to avoid, which is why pools may shut down when precipitation begins.

Reason #5: Accompanying Winds Can Fling Natural Debris and Pool Equipment

Last but certainly not least, rainstorms are frequently attended by volatile wind gusts due to the substantial changes in atmospheric pressure that characterize this type of weather.

If these wind gusts are severe enough, they can turn stationary objects into airborne projectiles, which can be extremely dangerous to swimmers. Poolside items such as poolside chairs, umbrellas, towels, and clothes can be tossed about, throwing everything and everyone in total disarray. Environmental debris, like twigs and leaves, may also be subject to the mercy of the winds.

Trying to institute order in such circumstances is near impossible, as everyone is only focused on gathering their personal belongings and racing to the nearest building. To avoid such chaos, lifeguards may make the call to evacuate the premises when the winds pick up in a rainstorm. This way, the problem can be resolved just before these winds become too much to handle.

It may be somewhat disappointing for the casual swimmer to evacuate if they’re not aware of the dangers of these wind gusts, but it’s better to be safe than sorry. If these wind gusts do end up being a fluke, the pool will simply re-open after the rainstorm has passed and the wind has come to a standstill.

Do All Swimming Pools Close When It Rains?

Public swimming pools are only mandated to close when lightning is nearby, not because of the rain itself. For this reason, swimming pools have varying policies toward pool closure if a rain shower does suddenly appear.

Typically, a drizzle will not be enough to warrant pool closure. More often than not, lifeguards will close the pool when the rain shower is so heavy that they’re unable to see the bottom of the pool. Under these circumstances, the aforementioned safety hazards become enough of an issue to warrant pool closure.

When lightning is involved, however, the rules regarding pool closure are more explicit. Lifeguards must close and evacuate the pool when lightning or thunder is within a six-mile radius of the pool (source).

To monitor just how close lightning has struck, lifeguards are instructed to use the Flash-to-Bang Rule. The premise of this strategy is to count how many seconds have gone by from the time lightning has been seen to the time the resulting thunder is heard. Based on the number of seconds that tick by, you can judge approximately how far the lightning is from your current location.

As a general rule of thumb, every five seconds counted from flash to bang is equivalent to a mile of distance between the lightning strike and your current location. You can use the following table for reference to link a flash-to-bang count to the approximate distance a lightning strike has been detected.

Flash-to-Bang Time CountRoughly How Far Away the Lightning Strike Was
5 seconds1 mile
10 seconds2 miles
15 seconds3 miles
20 seconds4 miles
25 seconds5 miles
30 seconds6 miles
35 seconds7 miles
40 seconds8 miles
45 seconds9 miles
50 seconds10 miles

From the table, you can see that any flash-to-bang count under 30 seconds should result in pool closure, as the lightning is a bit too close for comfort in these scenarios.

Anything above a 30-second count does not automatically warrant a pool closure, but certain pools may still close regardless. Even if the pool remains open, a lifeguard is typically posted on watch duty for another nearby lightning strike.

How Soon Can a Pool Re-Open After a Rain Shower?

Once a pool has been closed, there’s no guarantee that it will open back up again. If lightning and thunder are prevalent throughout the day, the associated safety risks outweigh the need to re-open the pool.

Nonetheless, there are certain circumstances where a rainstorm or thunderstorm will quickly pass through the danger zone, allowing the pool to re-open to the public.

To avoid re-opening the pool too quickly, lifeguards are instructed to wait 30 minutes after lightning has been detected in the area before even considering re-opening the pool. Then, if the thunderstorm has cleared away and there’s no further threat of lightning, lifeguards can safely re-open the pool. If lightning persists, however, the 30-minute count resets with each lightning strike that has been detected.

This rule regarding pool closing and re-opening procedure is so universal that it has actually earned the nickname of the “30-30” rule. To summarize this rule, any flash-to-bang count below 30 seconds results in pool closure, and a minimum of 30 minutes should pass by without any lightning strike for pool activities to resume (source).

If a pool has been closed solely due to heavy rains, lifeguards typically still allow at least 30 minutes to pass before re-opening the pool. This affords lifeguards ample time to clear any debris carried into the pool by volatile winds and ensure that there’s no separate rainstorm creeping in.

The last thing they want to do is resume normal pool activities and have another heavy rainstorm roll through. At the end of the day, swimmer safety takes precedence above all else.

The Bottom Line

Precipitation can result in pool closure, but not always. If a pool does close in the presence of rain showers, it’s often attributed to the hazardous threat of lightning, the danger presented by a slick pool deck, the greater likelihood of hypothermia, possible contamination of the pool, and airborne projectiles.

If the pool you’re swimming at does close when rain hits, refrain from taking your frustration out on the lifeguards. Ultimately, they’re just looking out for your own personal safety and those around you.

Sources: 1 2 3 4 5 6 7 8

Austin Carmody

I am the owner of HydroPursuit. I enjoy kicking back and getting out on the water as much as I can in my free time.

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