We often associate diseases like dysentery with the pioneers of old. Seldom do we hear stories like that happening in the 21st century. This is because of a major US public health initiative to disinfect public water supplies with chlorine. But is it completely safe? Isn’t chlorine toxic?
It’s a common question: if chlorine is poisonous, why do we put it in water? Today we’re going in-depth on why we use chlorine, its by-products, other disinfectants water treatment centers use, and more.
Why do we put chlorine in tap water?
Over 100 years ago, it was quite common for people to contract waterborne diseases like typhoid, Giardia, and a variety of viral infections. That is no longer as prevalent thanks to efforts to disinfect our drinking water, commonly with chlorine.
But it’s not as though folks before the 21st century were crossing their fingers every time they took a sip. They implemented public water treatment practices like filtration, chemical precipitation, and sedimentation. However, this wouldn’t guarantee that the water would be free of bacteria.
The first recorded case of water chlorination was in Maidstone, Kent, UK, in 1897, following an outbreak of typhoid fever from the local water supply. Chlorination gained traction in the United States after disinfecting a contaminated river water source in Chicago and another water supply in Jersey City in 1908.
A hypochlorite solution (diluted bleach, essentially) was the standard chlorinating chemical until the 1920s, when chlorine solutions and implementation technology advanced. The disinfecting process has become increasingly precise and controlled since.
Water must make its way from the treatment facility or source, through the pipes, and to your home. It needs something to keep it disinfected on its journey, and chlorine serves that purpose.
Is chlorine toxic?
On its own, chlorine is toxic in high concentrations. It may be harmful if inhaled or if it contacts your skin or eyes. However, if it’s mixed in water at a low concentration— 4 parts chlorine per 1 million parts water— it’s safe for use in drinking water.
Chlorine and chloramine have been a common part of the United States’ drinking water for 100 years. It allows most of the tap water that exits US taps to be drinkable without fear of waterborne illnesses.
However, most concerns with US drinking water lie in unforeseen long-term health effects. While there’s no research confirming effects from disinfectants in water, there are a few things to keep in mind, particularly with their by-products. It’s important to be informed about the water that makes its way to your home.
The biggest variable when it comes to water quality is the pipes and systems that are in your own home. Not all residencies receive water from a utility; it may look different for a well or private source. Some water sources, like deep groundwater, do not need disinfection.
Did you know that public water utilities are required to send annual water reports that disclose whether they maintained safe drinking water levels throughout the year? These reports must be out annually by July 1st, either by mail or online. You can find some of the reports at the EPA’s Consumer Confidence Reports database or by searching online for the name of your water utility plus “consumer confidence report.”
Additionally, the CDC has a helpful guide on how to read Consumer Confidence Reports. If you receive water from a utility and their chemical levels fall outside the safe range, they are required to send an alert.
Disinfectant By-Products
There is always debate over the best water purification method. One of the drawbacks of most chemicals is their disinfectant by-products, or DBPs. Some of the most common DBPs from chlorine include trihalomethanes and haloacetic acids.
In a nutshell, DBPs have long-term health impacts per the CDC and are therefore highly regulated. The Environmental Protection Agency, or EPA, learned about DBPs in 1974 and set requirements to regulate the amount in the water supply.
DPBs occur when chlorine contacts dirt or other contaminants. Therefore, part of the water treatment process includes removing these contaminants before the water is disinfected.
Other Disinfection Methods
Chloramine is a cross between chlorine and ammonia. It’s the second most common disinfecting chemical as it produces fewer DBPs than chlorine and is better at continuously disinfecting the water. However, it may increase nitrate formation and pipe corrosion with time.
Many utilities switch between chlorine and chloramine during the year. Using chlorine may create a biofilm (a layer of germ-protecting slime) on pipes over time. Switching to chloramine helps get rid of that biofilm.
Ozone and UV light disinfection are up for discussion as water disinfectants, but they have limitations. While these methods have disinfecting properties, they don’t work on murky or turbid water, nor do they continuously disinfect water from the treatment plants, through the pipes, to the tap. They also create their own DBPs.
What is the chloronitramide anion?
Back in the 1970s, the EPA was aware of the existence of an “unidentified product” in some drinking water sources. But research limitations back in the day kept this chemical from being brought to light. Quite recently, scientists identified and measured the product as the chloronitramide anion.
The chloronitramide anion is a DBP of water treated with chloramine. The study tested a significant number of US water sources. Obviously, it’s alarming to learn about chemicals we don’t understand in the water supply. But as of right now, there’s no reasonable cause for panic. Investigators don’t know how it affects human health, but research is underway.
Although not confirmed, there’s cause to believe that active carbon filtration may remove the chloronitramide anion from water— this is the method most at-home water filters use and removes many other DBPs.
So, is it safe to drink chlorinated water?
Yes, it is safe to drink chlorinated water. Sometimes, chlorinated water has an unpleasant taste or smell— it’s important that if the smell goes beyond a slight “pool smell,” you may have a plumbing issue. Regardless, there are a few methods to reduce the chlorine levels in drinking water.
Filtration with activated carbon is efficient at removing chlorine and DBPs from drinking water. These may be as intensive as reverse-osmosis machines that filter water in the home before it reaches the sink, or as simple as pitcher filters that you fill yourself.
One advantage of chlorine is that it’s volatile, meaning it evaporates more quickly than water. Letting tap water sit at room temperature for a while allows the chlorine to off-gas. However, this method may be time-consuming. Boiling water can speed up the process.
UV light can also further remove chlorine and chloramine from water. Ultimately, how or whether you choose to treat your water depends on your water utility, your home, and your available time and budget.
Final Thoughts
There are some parts of the water disinfection process that seem counterintuitive. While disinfectants keep us safe from biological threats in water, their use requires us to continue refining our purification processes to reduce any potential chemical drawbacks. At the end of the day, the worst thing you can do is not drink water at all.
If you have questions about chlorine or chloramine, the Missouri Poison Center is open twenty-four hours a day, seven days a week to take your call.
Frequently Asked Questions
Boiling can remove chlorine, but it’s not effective for chloramine, which is more stable and requires special filtration or chemical neutralization. If your water is disinfected with chloramine, look for filters certified to remove it specifically.
That “pool” smell comes from chlorine or chloramine reacting with organic matter in water or pipes. While not necessarily harmful at low levels, it may indicate higher-than-normal disinfectant presence or plumbing issues.
Yes. Fish, amphibians, and reptiles are particularly sensitive to chlorine and chloramine. Pet owners should treat tap water with dechlorinators before using it in aquariums or habitats.
Not always. Some bottled waters, especially those sourced from municipal supplies, may still contain residual disinfectants. Check the label or brand’s water quality report for details on treatment methods.
Distillation effectively removes chlorine, as it evaporates during the process. However, chloramine may persist unless the distiller includes a carbon pre-filter or other specific removal step.
Tap water is treated to be safe for drinking, not for use in your nasal passages. Tiny amounts of microbes, like Naegleria fowleri, can sometimes survive in treated water. They pose a risk when introduced directly into the sinuses, but would otherwise be killed by your stomach acids. Distilled, sterile, or previously boiled water ensures safety for neti pot use.
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Suggested APA citation:
Missouri Poison Center Trending Topics Blog. (2025, July 28). If Chlorine Is Poisonous, Why Is It in Tap Water?. Missouri Poison Center. https://missouripoisoncenter.org/if-chlorine-is-poisonous-why-is-it-in-tap-water/