Chlorine can kill germs on surfaces, but it's more effective at cleaning water- Here's why chlorine is better off in your pool
INSIDER 2hrs ago
a glass with a blue pool of water: Chlorine can kill germs, but alcohol is more effective. Bill Oxford/ Getty Images © Bill Oxford/ Getty Images Chlorine can kill germs, but alcohol is more effective. Bill Oxford/ Getty Images
  • Chlorine bleach products can be used to clean drinking water, pools, and countertops.
  • Chlorine can sometimes take up to 15 minutes to kill viruses, but alcohol kills most microbes within 10 seconds, which is why alcohol is a better choice for immediate disinfection.
  • However, chlorine is an effective household disinfectant when used in a product like chlorinated bleach.
  • This story is part of Insider's guide on How to Kill Germs.

Chlorine bleach is used in countless cleaning products. You've probably used chlorine while washing dishes, doing laundry, or cleaning your bathroom. Because chlorine is able to kill most germs, we also depend on it to disinfect our drinking water and clean the water in our swimming pools.

In the US, 98 percent of treated water supply systems use chlorine as a disinfectant.

Here's what you need to know about how chlorine kills germs.

When to use chlorine to treat water

When you add chlorine disinfectant to water, a chemical reaction occurs and a weak acid called hypochlorous acid is released. This acid is able to penetrate the cell walls of microbes like bacteria and viruses, so it can attack and kill germs effectively.

"Chlorine-based disinfectants are very effective against a wide range of viruses and bacteria, and under the right conditions even parasites," says Mary Ostrowski, senior director of chlorine issues at the American Chemistry Council.

Chlorine works by collapsing proteins in bacterial cells, which causes bacteria to die, Ostrowski says. Chlorine is also able to kill viruses, though the method it uses to kill viruses is less understood. Some experts think chlorine damages proteins inside virus cells, making viruses unable to get into human cells and cause infection. 

However, though chlorine can kill most germs, it does not always work immediately. This is one reason it works well for systems like pools and water tanks, which allow chlorine to sit in water over time. According to the Centers for Disease Control and Prevention, E. coli, a common bacteria spread through feces, dies in less than a minute when exposed to chlorine concentrations in a pool, while Hepatitis A, a serious virus affecting the liver, takes 16 minutes to kill.

Chlorine can take even longer to kill gastrointestinal parasites. A condition called Giardia takes 45 minutes to die, while Cryptosporidium, a serious diarrheal illness, takes 10.6 days to die after being exposed to chlorine.


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These timelines are longer than some other disinfectants like isopropyl or ethyl alcohol, which take about 10 seconds to kill most microbes. However, chlorine has the advantage of being able to kill bacterial spores, a dormant form of bacteria that can activate to cause infection.

Chlorine is a powerful disinfectant that can kill most bacteria, viruses, and parasites when it is added to water. If you want to use a chlorine product, make sure that you use the right concentration and give the chlorine enough time to take effect to ensure that all germs will be killed. 

The many uses of chlorine 

The biggest advantage of using chlorine to treat water is that it doesn't just kill germs at the moment it is applied, but continues to keep water clean over time, says Ostrowski.

"Chlorine protects treated water from re-contamination during its journey from a treatment facility through underground pipelines to our taps at home or elsewhere," Ostrowski says.

The chlorine used to treat drinking water is the same form that is used to treat pools, but the key difference is the concentration. In drinking water, chlorine is typically present in a concentration of 0.2 mg to 1 mg per liter.

In pools and hot tubs, experts recommend using between 1 mg and 3 mg per liter of chlorine.

Chlorine is also useful for cleaning household surfaces like floors and counters if present in a compound like chlorinated bleach. If you are using chlorine bleach for household cleaning, experts recommend using 1 cup of bleach per 5 gallons of water

People generally think of chlorine as a water disinfectant, but it is also used to purify other materials, says Ostrowski. Chlorine-based chemicals are used to purify the silicon in computer circuits as well as the titanium used to make artificial replacement joints.

Insider's Takeaway

Chlorine does not work as quickly as some other disinfectants like alcohol, but is more effective against certain forms of bacteria. Chlorine works better than other disinfectants for cleaning water, as it keeps water clean over time and won't hurt human health in low concentrations.

And if you're looking to kill bacteria on surfaces quickly and effectively, reach for chlorine-based bleach or alcohol-based disinfectants. 

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