Drinking Water Disinfection Byproducts: What They Are and Why They Matter
Disinfection is an important part of public drinking water treatment. It helps water utilities manage water quality as water travels from treatment plants through pipes to homes and businesses.
However, disinfection can also create unintended compounds known as disinfection byproducts, or DBPs. These byproducts may form when disinfectants such as chlorine or chloramine react with naturally occurring organic or inorganic matter in source water.
This guide explains what disinfection byproducts are, how they form, why they are monitored, and what households can do to better understand their local water quality.
What Are Disinfection Byproducts?
Disinfection byproducts are chemical compounds that may form during the water treatment process. They are not usually added directly to water. Instead, they can form when treatment chemicals react with natural materials already present in the water.
Common disinfectants used in public water treatment include:
- Chlorine
- Chloramine
- Chlorine dioxide
- Ozone
The type and amount of byproducts formed can depend on the disinfectant used, the water source, temperature, pH, treatment method, and how long water remains in the distribution system.
Why Is Water Disinfected?
Water disinfection has played a major role in improving public water systems. Before modern treatment practices, communities faced more frequent outbreaks of water-related illness.
Disinfectants are used because they help water utilities maintain water quality through the distribution network. They are especially important because water must often travel long distances through pipes, storage tanks, and local infrastructure before reaching the tap.
Chlorine and Chloramine
Chlorine and chloramine are two of the most common disinfectants used in public water treatment.
Chlorine
Chlorine is widely used because it is effective, practical, and provides a disinfectant residual that remains active as water moves through the distribution system.
One drawback is that chlorine may react with natural organic matter in source water, forming disinfection byproducts such as trihalomethanes and haloacetic acids.
Chloramine
Chloramine is formed by combining chlorine with ammonia. Some utilities use chloramine because it lasts longer in distribution systems and can reduce the formation of certain regulated disinfection byproducts compared with chlorine.
However, chloramine can also create operational challenges. For example, utilities must manage the risk of nitrification in distribution systems when ammonia is present.
What Is Nitrification?
Nitrification is a biological process that converts ammonia into nitrite and nitrate. In water distribution systems that use chloramine, nitrification can reduce disinfectant residual and affect water quality.
Factors that may influence nitrification include:
- Water temperature
- Water age in the distribution system
- Ammonia levels
- Disinfectant residual
- Pipe and storage tank conditions
Utilities manage nitrification through monitoring, system maintenance, water-age control, and treatment adjustments.
Common Types of Disinfection Byproducts
Many disinfection byproducts have been identified, but two major regulated groups are most commonly discussed in drinking water reports.
Trihalomethanes (THMs)
Trihalomethanes are a group of disinfection byproducts that may form when chlorine reacts with natural organic matter in water. Chloroform is one example of a THM.
Haloacetic Acids (HAAs)
Haloacetic acids are another group of regulated disinfection byproducts. The regulated group known as HAA5 includes five haloacetic acids that public water systems monitor.
Other Byproducts
Other byproducts may form depending on the disinfectant used and the chemistry of the source water. These can include chlorite, bromate, and other compounds monitored under specific regulations or research programs.
What Affects DBP Formation?
Several factors influence the formation of disinfection byproducts during water treatment and distribution.
- Type of disinfectant: Chlorine, chloramine, ozone, and chlorine dioxide can produce different byproducts.
- Organic matter: Leaves, soil, algae, and other natural materials can react with disinfectants.
- Bromide or iodide: These naturally occurring ions can influence the type of byproducts formed.
- Water temperature: Warmer water can increase reaction rates.
- pH: Water chemistry affects which byproducts are more likely to form.
- Water age: Longer time in pipes and storage tanks can allow more reactions to occur.
- Disinfectant dose: Higher disinfectant levels may affect byproduct formation.
Why Are Disinfection Byproducts Monitored?
Disinfection byproducts are monitored because long-term exposure above regulatory limits may be associated with increased health risks. Public water systems must balance two important goals: maintaining proper disinfection while minimizing regulated byproducts.
This balance is important. Reducing disinfectant too much can create other water-quality concerns, while excessive byproduct formation is also undesirable.
How Utilities Reduce Disinfection Byproducts
Water utilities use several strategies to reduce DBP formation while maintaining water quality.
- Removing organic matter before disinfection
- Optimizing disinfectant dose
- Managing water age in the distribution system
- Adjusting pH when appropriate
- Using alternative disinfectants when suitable
- Flushing distribution lines
- Monitoring seasonal source-water changes
The right approach depends on local source water, treatment plant design, regulations, and distribution system conditions.
How to Find DBPs in Your Local Water Report
Public water customers can review the annual Consumer Confidence Report provided by their local water utility. This report usually lists regulated contaminants detected in the water system, including disinfection byproducts when applicable.
Look for terms such as:
- Total trihalomethanes
- TTHMs
- Haloacetic acids
- HAA5
- Disinfection byproducts
- Stage 2 Disinfectants and Disinfection Byproducts Rule
If you do not understand the report, contact your water utility and ask for help interpreting the results.
Can Home Filtration Reduce Disinfection Byproducts?
Some home filtration technologies may reduce certain disinfection byproducts, depending on the system design, filter media, contact time, flow rate, and maintenance schedule.
Activated carbon is commonly used to improve taste and odor and may help reduce certain organic compounds, including some disinfection byproducts. However, performance varies by product.
If THMs, HAAs, or other DBPs are your concern, choose a filter based on documented performance information for the specific compounds you want to address.
Berkey Systems and Drinking Water Quality
Many households choose countertop gravity-fed filtration systems to improve the taste and odor of drinking water. Depending on the filter elements used, Berkey systems may help address certain common water-quality concerns.
For current filter options, review:
Always compare your water report or test results with current product performance information before choosing replacement elements.
Big Berkey Water Filter is our popular system.
Questions to Ask About DBPs
If you are concerned about disinfection byproducts, these questions can help guide your next steps:
- Does my utility use chlorine or chloramine?
- What are the reported TTHM and HAA5 levels?
- Do levels change seasonally?
- Does my home sit far from the treatment plant or near the end of a distribution line?
- What steps is the utility taking to manage DBPs?
- Is my filter tested for the specific DBPs I want to reduce?
Final Thoughts
Disinfection byproducts are an important water-quality issue because they are unintended byproducts of necessary treatment. Public water systems must maintain disinfection while also controlling regulated byproducts such as THMs and HAAs.
For homeowners, the best first step is to review the local annual water quality report. This can help you understand whether DBPs are present, how they compare with regulatory limits, and whether additional testing or filtration makes sense for your household.
Understanding disinfection byproducts can help you make more informed decisions about the water your family uses every day.
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