When water chlorination first began at the turn of the 20th century, it was hailed as an innovative solution to waterborne disease. Since if left untreated drinking water can carry pathogens that cause severe illnesses, the short-term health gains of chlorinated water were immediately clear. However, chlorination was quickly complicated by long-term health concerns, as scientist have identified what happens to the disinfectants as they react with other chemicals in our water. We want to take a look at these reactions and explore why they are a cause for concern.

Chlorine remains the chemical-of-choice for water disinfection within the United States due to its cost-effectiveness. However, it is widely understood that chlorination may result in some unintended consequences–one of which is that it can react with other things found in tap water (e.g. organic matter). These reactions can result in the formation of halogenated chemicals known as disinfection byproducts (DBPs). Many halogenated compounds are known carcinogens, so they rightfully receive quite a bit of scrutiny when found in tap water.

Some common disinfection byproducts include:

While over 600 different DBPs have been identified, they are still generally regarded to be “emerging contaminants,” since roughly 50% remain unaccounted for.

As the World Health Organization (WHO) states, “efficient disinfection must never be compromised” and the benefits of using a disinfectant take precedence of the longer-term risks of DBPs.

However, there are some major health risks from DBPs that result from long-term exposure.

While some disinfection byproducts have almost no toxicity, research shows that others have been associated with cancer, reproductive problems, and developmental issues in laboratory animals.

There are a variety of ways that DBPs can enter into the human body, including:

The Environmental Protection Agency (EPA) has developed a set of Disinfection Byproduct Rules to limit the public’s exposure to DBPs.

Additionally, Congress passed the Safe Drinking Water Act in 1974. Under SDWA, EPA sets the enforceable standards for drinking water quality–as well as monitors the authorities (States, agencies, and water suppliers) who enforce those standards. Some disinfection byproducts are subject to these legally enforceable standards, called a Maximum Contaminant Level (MCLs). While other disinfection byproducts (especially those still considered “emerging contaminants'), are subject to non-enforceable health goals (Maximum Contaminant Level Goals (MCLGs).

In order to limit DBPs, some US water systems are making the move towards using chloramine as a disinfectant. Chloramine has been deemed safer than chlorine for disinfection purposes, thanks to its tendency to produce fewer byproducts. However, while millions of American homes now receive chloramine-treated water, chlorine still remains the predominant disinfectant used in American water supplies.

While regulatory agencies are taking steps toward reducing disinfection byproducts (by pre-oxidizing or filtering out organic precursors), the most effective way to reduce your exposure is to filter your water at the point-of-entry so that you are protected from exposure via ingestion and inhalation (e.g., while showering or doing dishes).

Typically, a filtration system that includes activated carbon and is certified by the National Science foundation (specifically under the NSF/ANSI Standard 53 Certification for THMs) is a good choice. In addition to disinfection byproducts (such as THMs), activated carbon filters have been shown to successfully reduce chlorine and other compounds that may cause taste and odor issues.