One of the most prevalent chemicals in tap water is probably a familiar one; chlorine. That’s right, the same pungent chemical that stings your eyes after a day in the swimming pool and can kill your pet fish is the same one you’re ingesting in your tap water daily. Chlorine is highly effective as a water disinfectant, removing unwanted microorganisms. As a result, treatment facilities rely heavily on it to keep people safe from acute outbreaks of harmful microbes in municipal water supplies. The practice of water chlorination dates back to 1908, when chlorine was introduced to U.S. water systems to battle pathogens that caused waterborne diseases like cholera, dysentery, and typhoid fever. While those same water treatment plants do take steps to reduce chlorine from the water supply, much of it remains in the tap water that flows from our faucets. So, while we know this chemical is intended to create a safe drinking water source, what do detectable levels of chlorine in drinking water do to the human body?

Chlorine is commonly used as a bleach due to its strong oxidizing properties. Typical applications include disinfection, stain removal, and whitening, as the combination of chlorine bleach and water breaks down organic compounds, destroying stains and discoloration. Chlorine bleach is widely used in laundry detergents, household cleaners, and, you guessed it, drinking water treatment. Chlorine, as a disinfectant, typically exists in two forms: a gas and a liquid. The former is widely used in industrial settings, such as in the production of chemicals and plastics. The CDC warns about the harmful effects of chlorine gas, with some of the listed side effects being difficulty breathing, skin irritation, severe airway irritation, and even death. The handling of chlorine gas requires specialized equipment and safety precautions. And while the liquid state of this chemical used in water disinfection has a significantly reduced acute toxicity than its gaseous counterpart, it begs the question: is this chemical really safe to consume in any form?

Research in this area has grown over the last few years, but the dangers of chlorine have been assumed for decades. So what is one of the more concerning effects of chlorine in drinking water, you ask? You guessed it: cancer.

The chlorine disinfection process results in chlorine disinfection byproducts (DBPs) known as trihalomethanes (THMs) and haloacetic acids (HAAs), which are listed as probable human carcinogens.

The Delaware Division of Public Health reports that while these chlorine byproducts do not pose an acute risk to public health, long-term repeated exposure to low levels is likely linked to bladder and colon cancer, and higher levels of exposure may even cause reproductive problems and congenital disabilities.

A 1980 study by the U.S. Council of Environment Quality reported that the risk of cancer is 93% higher for those in contact with chlorinated water. So that certainly got our attention.

The current allowable amount of chlorine in your drinking water is 4 mg/L, while the maximum permissible level for total trihalomethanes is only 0.080 mg/L, and haloacetic acids is 0.060 mg/L.

If you want to learn more about how the EPA sets water quality standards for certain contaminants, read our Maximum Contaminant Level blog. (It might surprise you to learn that health effects are only one of three considerations in determining allowable levels of chlorine and other chemicals.)

But don’t get too comfortable thinking these probable carcinogens are highly regulated and therefore pose no health concern. The World Health Organization has stated, “In all circumstances, disinfection efficiency should not be compromised in trying to meet guidelines for DBPs, including chlorination byproducts, or in trying to reduce concentrations of these substances.” According to them, “The risk of not disinfecting drinking water—and exposing people to microorganisms that can cause illnesses—outweighs the long-term, low-level risk of DBPs, particularly at the low levels typically found in U.S. water supplies.” And while we agree water disinfection is of the highest priority, potentially exposing populations to known carcinogens at higher than normal levels in that pursuit shouldn’t be an acceptable solution.

It’s worth noting that the risk of cancer from exposure to DBPs in drinking water is generally considered small compared to other known risk factors, such as smoking or exposure to air pollution. Nevertheless, the EPA and other public health organizations recommend minimizing exposure to DBPs in drinking water by using effective water treatment methods and ensuring that drinking water meets regulatory water quality standards for DBP levels.

Additionally, some people use a water filtration system to reduce their exposure to chlorine, DBPs, and other potential contaminants. The truth is, once chlorinated water reaches your home, the chlorine has delivered clean water free from waterborne pathogens. Therefore, there is no benefit to leaving your water chlorinated for consumption. The research clearly shows some significant drawbacks to not running it through a water filter first.

Every one of the filters produced by Clearly Filtered is expertly designed to significantly reduce both Free Chlorine and Total Chlorine from your water. The filters used in our water pitchers, water bottles, and Under the Sink units remove up to 99.5% of chlorine; well beyond anything water treatment facilities can achieve.

So, while chlorine provides a benefit, it comes with a cost. With Clearly Filtered, you can eliminate that cost and make sure that you and your family drink water that is carcinogen-free. Drink water that is clean and safe. Drink Clearly Filtered.