There are real benefits to adding chlorine to water. We can thank the element for our safe hydration and relatively germ-free swimming pools. But a recent study published in Environmental Health Perspectives noted a significant downside: Although chlorine is used to disinfect water, it can create byproducts when reacting to the natural organic matter in the water (think leaves, twigs, etc.). One of these byproducts, called trihalomethanes (THMs), is known to have carcinogenic properties—aka substances that may increase your cancer risk.

Are These Findings Cause For Concern?

It’s important to note that THMs are regulated both in the United States and in the European Union. In the U.S., THMs are limited to 80 parts per billion (ppb), while the E.U.’s limit is 100 ppb. For reference, drinking water typically falls somewhere between 40-60 ppb, according to the EPA. While these regulations are certainly a start, it doesn’t seem that they are sufficient or even regularly followed. Thousands of people across the United States are drinking water contaminated with upwards of 200 ppb of THMs, according to data from the Environmental Working Group (EWG).

Unfortunately, this study found that increased cancer risks begin at just 40 ppb, meaning your everyday drinking water may be causing some damage. EWG determined the safe level of THMs consumption to be much lower—only 0.15 ppb. While THMs’ adverse impact on health is nothing new, the new study shows that these compounds can have this impact at lower levels than originally thought, explains the founder of Hydroviv, Eric Roy, Ph.D.

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Of note, the study suggests that THMs can increase the risk of both bladder and colorectal cancer. After collecting data from roughly 30 different studies conducted on 90,000 participants, they also found that men are more at risk than women.

“While further studies are needed to assess which THM compounds are riskiest and the levels at which we see an impact to human health, this study may be the first step in refining the optimal levels of chlorination in our public water supply,” adds Dr. Brintha Vasagar.

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So Why Is Our Water Chlorinated If It Can Cause Harm?

“It is important to remember that we chlorinate water for good reason: to disinfect it from microorganisms,” says Dr. Vasagar. “While THM levels would drastically fall if we stopped chlorinating water, the resulting disease would be staggering.” Indeed, there is good reason why we chlorinate our water. The introduction of clean water (aka chlorinated water) is “responsible for cutting three-quarters of infant mortality and nearly two-thirds of child mortality in the United States in the first 40 years of the 20th century—the most rapid health improvements in the nation’s history,” according to the Population Reference Bureau (PRB). Dr. Roy stresses that tap water chlorination is one of the biggest public health achievements of all time. It is largely responsible for eliminating deaths from diseases like typhoid fever, pneumonia, and tuberculosis. This is why it’s important to continue to add chlorine to drinking water despite potentially adverse side effects, Roy continues. “The trouble is, it’s hard to predict how high levels of chlorination will impact any one person,” he explains. “Some people can drink unfiltered tap water their entire life with little to no adverse reaction, while others may develop illnesses later in life.”

How Can You Protect Yourself?

There are numerous ways to decontaminate your drinking water. Vasagar recommends boiling water or using carbon filtration or reverse osmosis systems, which double-filters water through a semi-permeable membrane. “Boiling water is the cheapest but most time-intensive, carbon filtration is the best balance of water purity for cost, and reverse osmosis ensures the purest water but is the most expensive,” she explains. She further cautions people who have an increased risk of bladder or colorectal cancer to take advantage of these systems.

“Most importantly, early detection can be key, so be sure to see your family medicine physician at least once a year, or sooner if you notice blood in your stool or urine, unexpected weight loss, or are generally feeling unwell,” she says.