Until the 20th century, waterborne diseases were a common part of everyday life and one of the leading causes of death. Many believed that good-tasting water meant clean water, but in reality, even the freshest-tasting water could contain disease-causing microorganisms. It was during this period that drinking water disinfection began, aiming to eliminate viruses, bacteria, and other harmful microorganisms.

Water disinfection is critically important to make water safe and to protect consumers from infectious diseases such as cholera, typhoid fever, and many others. However, disinfection also has its downsides and is associated with certain health risks. In this blog, we’ll explain why and discuss ways to address these challenges.

Disinfection takes place at water treatment facilities, and only after that is the water distributed through the supply network. The water delivered to consumers must always be protected by disinfectants to ensure pathogens are neutralized and prevented from multiplying under any conditions. For this reason, it is essential to use effective disinfecting agents, such as chlorine or chloramine — the latter produced by mixing chlorine with ammonia.

In addition to chlorine and chloramine, there are several other disinfection methods that effectively combat disease-causing microorganisms. These include ozone treatment, chlorine dioxide, and ultraviolet (UV) irradiation. Each water system has its own unique characteristics, which must be considered when choosing the most appropriate disinfection method.

How Do Disinfection Byproducts Form in Water?

Apart from ultraviolet (UV) irradiation, most other disinfection methods used in water treatment lead to the formation of disinfection byproducts (DBPs), which can pose certain health risks.

The disinfectant chemicals mentioned above react with naturally occurring substances already present in the water. These substances often appear as a result of processes such as the decomposition of leaves, plants, or pesticides. Additionally, water may contain industrial waste, pharmaceutical residues, plasticizers, and other contaminants. When disinfectants interact with these compounds, disinfection byproducts are formed.

When disinfecting with chlorine, these byproducts are generally divided into two main groups:

• Trihalomethanes (THMs) – including chloroform, bromoform, bromodichloromethane, and dibromochloromethane
• Haloacetic acids (HAAs) – including monochloro-, dichloro-, trichloro-, monobromo-, and dibromoacetic acids.

However, it is important to note that these products have not been fully studied, and experts believe that less than half of all existing byproducts have been identified so far.

The concentration of disinfection byproducts in drinking water varies daily and depends on multiple factors — such as the season, water temperature, the amount of disinfectant used, the types of substances present in the water, and more. Moreover, the longer water remains in the distribution system, the more time disinfectant chemicals have to react with organic and inorganic compounds, leading to higher levels of byproducts.

Health Risks: What You Need to Know

The disinfection byproducts (DBPs) formed when disinfectant chemicals react with naturally occurring substances in water can pose certain health risks. This applies not only to drinking water but also to any water we come into physical contact with — including bathwater, swimming pool water, and even food prepared using tap water.

A 2020 study identified potentially carcinogenic chemical compounds produced when chlorine reacts with substances naturally present in water. These compounds include not only organic matter but also human-activity-related contaminants such as phenols, plasticizers, sunscreen components, and antimicrobial agents.

It is worth noting that fewer byproducts are generally formed when using disinfectants other than chlorine. However, the long-term health effects of these compounds are still not fully understood. Scientists believe that other disinfectants may also lead to the formation of yet-undiscovered byproducts, some of which could also be harmful to human health.

For example, a 2024 study detected a previously unknown byproduct — chloronitramide anion — in a water treatment system that used chloramine for disinfection. While the toxic effects of this compound remain unclear, its chemical structure suggests potential health risks, similar to other known disinfection byproducts.

This creates a delicate balance between two risks: On one side are disease-causing pathogens, which can be life-threatening if water is left untreated. On the other side are long-term health risks associated with low concentrations of disinfection byproducts.

Finding the right balance between these two is one of today’s greatest challenges, especially amid population growth, climate change, and the increasing mixing of wastewater with freshwater sources. Nevertheless, solutions do exist, and ongoing research is working toward safer and more sustainable disinfection methods.

How to Protect Yourself from Existing Risks

There are several strategies that can significantly reduce the concentration of disinfection byproducts (DBPs) in drinking water:

One approach is to thoroughly filter water before the disinfection process. Another is to remove organic compounds from water prior to chlorination, which helps minimize the formation of DBPs.

Thus, water disinfection and the reduction of its byproducts present a complex but solvable challenge. The solution lies in preventive approaches and advanced technological solutions, which include:

• Protecting water resources from pollution at the source
• Improving filtration systems to enhance water quality
• Implementing advanced disinfection technologies
• Ensuring regular online and laboratory monitoring
• Involving qualified engineering companies to design and optimize filtration systems

For effective monitoring, it is crucial to use reliable water analytics tools that ensure both accurate results and efficient application. In this field, HACH is the global leader, producing high-quality water analysis equipment, including:

• Chlorine analyzers — used to accurately measure chlorine levels in water
• BioTector online analyzers — continuously monitor the total organic carbon (TOC) concentration in water to reduce organic matter before it reacts with chlorine
• UVAS plus ultraviolet sensors — provide reagent-free measurements of dissolved organic substances, protecting water treatment processes from excessive organic loads
• Portable turbidity meters — used after chemical treatment to monitor the remaining organic compounds in water; low turbidity indicates that most organics have settled out, minimizing DBP formation
• Activated carbon cartridges — applied before chlorination to remove organic substances from water

Technological progress, combined with the implementation of advanced water treatment processes and effective management systems, offers hope that safe and clean water will become accessible globally in the near future.