Disinfection Byproducts In Drinking Water: Toxicity, History, and Policy
What Are Disinfection Byproducts?
Why Do We Care About Disinfection Byproducts?
Many halogenated organic compounds are known carcinogens in humans (e.g. dioxin, DDT, Carbon Tetrachloride, PCBs), so they rightfully receive quite a bit of scrutiny when generated in tap water. While some disinfection byproducts in water have almost no toxicity, others have been associated with cancer, reproductive problems, and developmental issues in laboratory animals. Some population-scale epidemiology studies have also found an association between chlorinated tap water and these same problems in humans. Because more than 200 million people in the US use chlorinated tap water as the primary drinking water source, it’s something worth taking a very close look at.
How Are Disinfection Byproducts Regulated?
History Of Disinfection Byproduct Regulation
In 1974, trihalomethanes were detected in drinking water and linked to chlorine based disinfectants that were added to municipal tap water. Around the same time, the National Cancer Institute classified trihalomethanes as human carcinogens, and as a result EPA established a drinking water standard for trihalomethanes in 1979. As more was learned about disinfection byproducts in water, the US EPA and other government, public health, and industry stakeholders began negotiating 2 stages of more comprehensive regulations in the mid-1990s. Stage 1, which was published in 1998 for 2002 compliance, ruled that haloacetic acids must also be monitored in tap water, in addition to trihalomethanes. The Stage 1 Rule also mandated that these chemicals be monitored throughout the entire water distribution system, not just a few predefined sampling locations. The results of the increased monitoring revealed that more municipalities were non-compliant than initially expected. Stage 2 of the regulation was published in 2006 (for 2012-2016 compliance), and further refined the sample collection strategy with the goal of protecting the public. In the future, most people expect that the regulations will continue to tighten as more about the long term effects of these chemicals becomes better understood, and the technologies that reduce their concentrations at the municipal level improve.
How To Know If A Municipality's Tap Water Has High Levels of Disinfection Byproducts
Overall, disinfectant byproduct concentrations are difficult to predict, because many factors influence their formation including: concentration of organic matter, chemical composition of the precursor materials, pH, temperature, type of disinfectant used, and the concentration of disinfectant. However, because monitoring for trihalomethanes and haloacetic acids are mandated by the EPA, the average concentrations found in the water supply must be made available to the public in annual drinking water reports.
Within a given municipal water system, different physical locations can have higher disinfection byproduct concentrations than others, based on where the home or business is located. This is because the longer it takes for the water to reach the home, the more opportunity there is for disinfection byproducts to form. Therefore, locations close to fast flowing water mains often have lower levels of disinfection byproducts than homes found at the periphery and low flow areas of the water distribution network. Additionally, disinfection byproduct concentrations can continue to rise in residential pipes/water tanks if the water remains stagnant for extended periods of time (e.g. during the work day, overnight). In fact, most municipalities recommend letting water run for 1-10 minutes before using it for drinking or cooking so pipes can flush out. (Obviously, nobody does this….)
What Are The Primary Ways That People Are Exposed To Disinfection Byproducts In The Home?
In the home, most people primarily use chlorinated tap water to drink, bathe, wash dishes, etc. A few studies have looked at the relative importance of the various exposure pathways, and found that showering contributed heavily to blood levels of trihalomethanes. While this may be initially surprising, it does make sense, because trihalomethanes can be volatilized in hot water and subsequently inhaled. During a shower, disinfection byproducts can also enter the body through absorption through the skin. Because most people come in contact with over 17 gallons of water in an “average” 8 minute shower, but drink less than a half-gallon of water each day, it makes sense that showering can be a major exposure path. Granted, this study only looked at the exposure route for one class of disinfection byproducts, but it does reveal that exposure pathways in addition to drinking, and is a great discovery to build upon with follow-up studies.
What Can Individuals Do To Reduce Their Exposure To Disinfection Byproducts?
To be clear, the discovery of DBP exposure through showering does NOT mean that you should be afraid of showering, rather it's a piece of information that may be considered in any changes to the regulation. As frustrating as it may be to people "looking for answers," the reality is... good science is a slow process... and modifications to regulation are often even slower! While regulatory agencies and municipalities are taking steps toward reducing DBPs in water (by preoxidizing or filtering out organic precursors), the most effective way for consumers to reduce their exposure today is by filtering their water at the point of use, and/or by flushing stagnant water out of the pipes by letting it run for a few minutes before using it.
1) http://www.epa.gov/_ (and sources therein) Accessed on 12/25/2015
3) Backer, LC, et al., 2000
4) Richardson et al., 2007.
Other Great Articles From Water Smarts Magazine:
Should I Use A Shower Filter?
About a year ago, I moved to Washington, DC, and learned that a number of my friends (also transplants) used shower water filters because they had similar issues with city water. I also learned from them that the products they used were not living up to claimed longevity and performance. Because Hydroviv was determining our product roadmap at the time, a heavy-duty shower water filter was added to the planned product line, and we ended up finishing it first.
- A Creative Director for a salon in Arizona wants to avoid detrimental effects of chlorinated water on hair and to increase the effectiveness of styling products
- A model in NYC has noticed that her hair and skin have suffered since moving to NYC, and wanted to improve both
- A family in Maine wants to remove offensive odors from their well water
- Numerous people with sensitive skin (like myself) want to reduce skin irritation that occurs during showering
As always, if you have any questions, send them to email@example.com or leave a comment below.
Tap Water Chlorination: The good, the bad, the unknown
The GoodShortly after scientists in the 1800s demonstrated that microorganisms are responsible for many diseases, people began experimenting with ways to disinfect water. Fast forward to 1908, Jersey City began injecting chlorine into the public tap water supply, which marked the beginning of large-scale water disinfection in the United States. Since then, disinfection practices have become commonplace in the developed world, and the spread of waterborne illness through public water supplies has come to a screeching halt. This is a very good thing.
The BadBy design, chlorine-based disinfectants (like bleach) cause damage to living things, otherwise they wouldn’t be effective. Of course, chlorine-based compounds don't kill humans at concentrations found in tap water, but there are known side effects of consuming and showering in chlorinated water, including skin,eye & stomach irritation. While the allowable chlorine levels set by EPA at a level low enough so they don’t cause adverse effects in the majority of people, some people (myself included) are sensitive to chlorine-based chemicals found at concentrations allowed in tap water.
In addition to these negative “health based” side effects, there are other “nuisances” caused by chlorine in water. For example, anyone who has spent time in a chlorinated pool or hot tub knows that chlorine-based chemicals can cause hair and clothes to fade (picture below), and a quick Google search reveals plenty of reasons for using purified water for things like watering houseplants, watering gardens, and filling fish tanks.
The UnknownHere's what we know:
- We know that untreated water can transmit waterborne disease (e.g. dysentery, Cholera, E. coli …)
- We know that disinfecting water with chlorine-based chemicals greatly minimizes this risk.
- We know that the known side effects of chlorine-based disinfectants are minor when compared to the risk of waterborne disease.
However, as is the case with most things, our understanding of water quality is still progressing. A great deal of research is currently focused on a class of chemicals referred to as "disinfection byproducts." Simply put, disinfection byproducts are the chemicals that form in water when chlorine-based disinfectants react with organic matter.
Scientists are still studying the chemistry and toxicology of these compounds, but what we do know suggests that these chemicals may not be great for us over the long term.
A separate blog post on this topic is forthcoming.
Here’s additional information about the two types of chlorine-based disinfectants used in DC's water supply (as well as many other municipalities):
About 25% of municipalities in the US (including Washington, DC) use chloramine (also known as combined chlorine) as the primary public water supply disinfectant. Chloramine is formed by adding ammonia to chlorinated water. Chloramine (like chlorine) is an effective disinfectant, and it's effect is persistent in the distribution system due to its low volatility. However, this persistence makes it so chloramine does not "go away" if you leave an unsealed container in the fridge overnight, so we have to deal with the associated taste and odor.
Chlorine:DC's tap water switches over to a chlorine disinfection cycle for a few weeks each spring. This more aggressive "spring cleaning" kills any microbial buildup that may have occurred throughout the distribution system. During these few weeks, many DC residents notice a change in their tap water's taste and odor. Fortunately, because chlorine is more volatile than chloramine, the unpleasant taste/odor is minimized if you let a container of water sit out overnight.
As always, feel free to comment on this post or email firstname.lastname@example.org to let us know what you are thinking!
Other Great Articles From Water Smarts Magazine:
Fluoride in Municipal Tap Water: What You Need to Know
Lead Contamination in Flint, MI Drinking Water: Why it Could Happen in Your City?
Anatomy of DC's Tap Water
The Washington Aqueduct (Army Corps of Engineers)and DC Water (District of Columbia Sewer and Water Authority or DC WASA) are the two government entities that produce and distribute Washington D.C.’s tap water. The Washington Aqueduct collects water from the Potomac River, treats it, and sells it to DC Water, and DC Water is responsible for distributing the water to homes and businesses in DC, as well as maintaining water quality standards along the way.
DC WASA does much more than “keeping the pipes flowing” (which with more than 1300 miles of pipe is a logistical feat on its own), they also employ a team of dedicated water quality experts, all working to ensure that water quality meets or exceeds standards set by US EPA. This means running 24/7 compliance (tests that they are legally obligated to do) and voluntary (above and beyond) monitoring programs throughout the city. One interesting aspect of this voluntary program is maintaining mobile laboratories that are staffed with technicians that can be dispatched to investigate emergencies and respond to customer complaints.
DC WASA also puts a great deal of time and effort into community engagement and public awareness. DC WASA participates in over 100 community outreach events each year to help customers understand the valuable water services they provide. One example of these programs is the Clean Rivers Project, where DC WASA promotes best practices practices to minimize the amount of sewer overflow that is discharged into D.C.'s waterways. In addition to managing a water education program for District students, DC WASA hosts annual town hall meetings in every ward of the city.
Throughout my career, I’ve had the opportunity to work with a number of municipalities (both large and small), and DC WASA does a very good job with information transparency. I would encourage all residents to check out their website (www.dcwater.com) for more information, which includes things like: water quality reports, overall strategic plan, and the role that residents play in maintaining water quality within their own home.