Chlorine is like a medication with side effects: a necessary evil. But how necessary is it? And how evil can it be? 

On one hand, it’s been protecting us from waterborne diseases for more than a century. On the other hand, swallowing the same chemical that bleaches your clothes probably isn’t anyone’s idea of “healthy.”

Let’s dive in.

Before 1908, drinking tap water was a gamble with death... 

The U.S. EPA didn’t exist (it wouldn’t until 1970), the Safe Drinking Water Act was decades away (1974), and waterborne diseases like cholera, typhoid fever, and dysentery killed thousands of Americans each year.

Then, in 1908, a New Jersey court ordered the Jersey City Water Supply Company to solve the city’s typhoid epidemic. That’s when Dr. John L. Leal proposed a radical solution: add chlorine to the water supply.

Typhoid rates plummeted, word spread, and within a few years, utilities across the country followed suit. By the 1940s, the usual large-scale outbreaks of waterborne diseases had basically disappeared. 

That’s why, today, disinfection is standard. 

Utilities add a small amount of chlorine or chloramine (a chlorine-ammonia disinfectant) to our tap water as a “final barrier” between the treatment plant and your tap—killing bacteria, viruses, and other microorganisms that could otherwise make us sick. 

Chlorine itself is actually regulated by the U.S. EPA (with a Maximum Residual Disinfectant Level of 4 milligrams per liter), and is generally considered safe at the levels used in drinking water. But here's where it gets complicated: When chlorine does its job—killing germs—it also reacts with naturally occurring organic matter in water. 

The result is chlorine’s no. 1 side effect: chemical compounds called disinfection byproducts, or DBPs. 

Hundreds of DBPs can form when chlorine or chloramine come into contact with certain organic material (like leaves, algae, dirt, and pesticides). These DBPs include cancer-linked total trihalomethanes (TTHMs) and haloacetic acids (HAA5), as well as emerging dangers such as NDMA, iodoacetic acid, and chloronitramide anion.

Let’s take a look at each.

A 2025 analysis out of Sweden reports that THM exposure may increase the risk of bladder cancer by 33% and colorectal cancer by 15%—even at levels below today’s legal limits. Some studies also link THMs exposure to an increased risk of miscarriages. 

While the U.S. limits TTHMs in drinking water to 80 ppb (parts per billion), the Environmental Working Group (EWG) recommends not exceeding 0.15 ppb to protect the public from cancer. 

That means the EPA allows up to ~533x more TTHMs in our tap water than what EWG experts consider safe.

HAAs are another family of disinfection byproducts. Five of them (HAA5) are regulated, but dozens more aren’t. Unlike THMs, HAAs don’t readily evaporate. That means boiling doesn’t remove HAAs and may even concentrate them as water evaporates.

Like THMs, long-term exposure to some HAAs has been linked to higher risks of multiple types of cancers, including bladder, liver, colon, and rectal cancer. HAAs have also been associated with liver and kidney effects, as well as developmental and reproductive concerns. 

While the U.S. limits HAA5 in drinking water to 60 ppb, the EWG recommends not exceeding 0.1 ppb to protect the public from cancer. 

Besides the familiar DBPs (THMs and HAA5), several new and emerging DBPs are raising fresh health concerns…

Here are just a few examples: 

• NDMA (N-nitrosodimethylamine) is a probable human carcinogen estimated to be almost 600x more toxic than any THM. Some water utilities have switched from chlorine to chloramine in an effort to reduce the formation of THMs. Ironically, NDMA is likely an unintended side effect of making that switch. 

• Iodinated DBPs (e.g., iodoacetic acid) have shown dangerous effects in lab tests, even at very low levels. The concern with iodoacetic acid is that even tiny amounts can damage cells and DNA, which raises red flags about cancer risk and other health problems. However, more research is needed to fully understand its impacts. 

• Chloronitramide anion has officially been identified. Found in water supplies serving over 100 million Americans, its toxicity is unknown, but early computer models suggest it could be harmful. No official safety studies exist yet, and experts emphasize the urgent need for more research to understand its risks.

What makes these emerging DBPs worrying isn't just their potential toxicity, but that we could be exposed to them daily while their safety remains a complete unknown.

We’ve seen this story before with contaminants like PFAS: early unregulated exposure turned out to cause widespread harm for many.

Some emerging DBPs might end up being just as harmful, others less so. But until research catches up, it’s almost like we’re drinking an experiment at times.

According to the U.S. EPA, the risk from not disinfecting drinking water—leaving people exposed to potentially deadly pathogens—outweighs the potential long-term risks posed by disinfection byproducts (DBPs). Or like we said before, what's worse: Chlorine in your water, or water without chlorine?

The answer isn't simple: Infrastructure limitations, cost considerations, and regulatory momentum make replacing chlorine a tall order. 

Most U.S. water systems were built around chlorine-based disinfection, and retrofitting thousands of treatment plants would cost billions. Plus, chlorine works. It's cheap, effective, and provides lasting protection as water travels through miles of pipes to your tap.

But other approaches exist. 

Countries like Germany, Switzerland, and Austria focus on preventing contamination rather than killing it after the fact. 

They invest heavily in source water protection—keeping pollution out of rivers and lakes in the first place. They use advanced treatment like ozonation and UV light, and employ multiple barriers instead of relying primarily on chemical disinfection. Some Swiss systems use minimal or no chemical disinfectants at all.

What’s the trade-off? 

Higher upfront costs and more complex operations. However, the result is clean water with fewer chemical byproducts, proving that our current system isn't the only way.

However, replacing chlorine won’t happen overnight—if ever. 

So what can you do now, today, to protect yourself and your loved ones from chlorine and its side effects?

While ordinary carbon water filters may target chlorine, they can’t protect you from the real problem: DBPs like THMs and HAA5. To keep those dangers out of your glass, you need specialized filtration.

That’s where Clearly Filtered comes in... 

Powered by breakthrough Affinity® Filtration Technology, our entire line of advanced water filtration systems are proven to protect you from chlorine. Plus, our best-selling filtered water pitcher goes even further to protect you from Trihalomethanes (THMs), Haloacetic acids (HAA5), and hundreds of other dangers ordinary filters overlook. 

Protect yourself and your loved ones by upgrading to Clearly Filtered today.