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Chlorine in Our Drinking Water - A Cause For Concern

Protecting the majority of the US drinking water from disease causing bacteria, viruses, and other microbes, are disinfectants such as chlorine, chloramines, ozone, and chlorine dioxide.  This practice of disinfection has been in place since the early 1900's, and Chlorine is a chemical that has played a significant role.  Over the past few decades, numerous studies have been conducted by members of the scientific, regulatory, and public communities evaluating the short and long term safety of chlorination. While some have shown no negative effects on human health, there are many that have.

History of Chlorine

Chlorine has made it's mark on history by virtually eliminating water borne diseases and allowing populations around the world to flourish.  It easily applied at the water source and small amounts have the ability to be effective throughout a municipal distribution network, from the water treatment plant all the way to the faucet tap.  The discovery of these benefits coupled with it's low cost resulted in chlorine being chosen as the preferred chemical for both domestic and industrial purposes for most of the 20th century.


Concerns Over Chlorine in Drinking Water?

Concerns over chlorine stem from the way in which the chemical reacts with organic plant matter that is naturally present in water, in addition to it's reactions with saliva and stomach content when ingested.  These chemical reactions result in a group of chemicals known as disinfection byproducts(DBPs).  Some of my readers may be familiar with one of the most notorious byproducts called Trihalomethanes (THMs) which consist of four chemicals: chloroform, bromodichloromethane, dribromochloromethane, and bromoform.  Scientific evidence classifies THM's as known carcinogens with two types of health effects being shown by studies; organ cancer and reproductive/developmental health effects.  The following paragraphs highlight some of these findings.

World Health Organization Study

Released in 1996, and republished again in 2003, the World Health Organization (WHO) released a study of Chlorine and it's water reacting equilibrium forms of hypechlorous acid and hypoclhorites and their effect on mice and rats. In these studies, short terms chemical exposure seemed to indicate no negative effects on the mice.  However, 2 year long term rat exposure to sodium hypochlorite in drinking water resulted in a "dose related depression in body weight gain in all groups, depressed liver, brain, and heart weights in males given a .05% dose, decreased salivary gland weights in both female groups, and decreased kidney weights in females given .2%."  Also shown was that oral administration of Chlorine via hypochlorite ion or hypochlorous acid at 100, 200, 400 mg of Chlorine/liter resulted in "dose-related increases in the amount of sperm-head abnormalities in male mice."  Towards the end of the WHO Guideline for drinking water quality, under the heading "Effects on Humans", the WHO study referenced 2 studies reading the following:

"In a study of 46 communities in central Wisconsin where chlorine levels in water ranged from 0.2 to 1 mg/litre, serum cholesterol and low-density lipoprotein levels were higher in communities using chlorinated water. Levels of high-density lipoprotein (HDL) and the cholesterol/HDL ratio were significantly elevated in relation to the level of calcium in the drinking-water, but only in communities using chlorinated water.  The authors speculated that chlorine and calcium in drinking-water may interact in some way that affects lipid levels." And, from another study, "An increased risk of bladder cancer appeared to be associated with the consumption of chlorinated tapwater in a population-based, case–control study of adults consuming chlorinated or non-chlorinated water for half of their lifetimes."

Additional Studies on Chlorine

In the 1960's, Joseph M. Price, MD performed experiments using chlorine in the drinking water of chickens. He came back to report that 95% of the chickens given chlorine added to distilled water developed atherosclerosis within a few months. In his book, Coronaries/Cholesterol/Chlorine, Dr. Price presented alarming evidence that Trihalomethanes (THMs), are the "prime causative agents of arteriosclerosis and its inevitable result, the heart attack or stroke."

In the summer of 1992, the New York Times reported on a study directed by Robert D. Morris of the Medical College of Wisconsin in Milwaukee, compiling 10 separate epidemiological studies from the 1970's on chlorinated drinking water. Morris partnered with with epidemiologist Thomas C. Chalmers and his colleagues at Harvard to utilize a statistical technique call meta-analysis. They reported that people drinking chlorinated water over long periods had a 21% increase in the risk of contracting bladder cancer and a 38% increase in the risk of rectal cancer. "I am quite convinced, based on this study, that there is an association between cancer and chlorinated water." said Morris.

Taking a Chlorine Shower

According to researcher Bruce Black - Chlorine and Your Shower,  "Taking long hot showers is a health risk--and to a lesser extent baths. They lead to a greater exposure to toxic chemicals contained in water supplies than does drinking the water. The chemicals evaporate out of the water and are inhaled. They can also spread through the house and be inhaled by others. House holders can receive 6 to 100 times more of the chemical by breathing the air around showers and bath than they would by drinking the water."

Chlorine and The EPA

In official publications, the EPA has concluded that there is evidence to support a potential association between long term exposure to high levels of THMs and bladder cancer as well as suggestions of an association with colon and rectal cancers. However the EPA notes that health effects data for the reproductive and developmental health effects are inconclusive and do not show causality. In 1980, the EPA adopted new regulations requiring cities to reduce chlorination by-products (THM's) in the water to less than 100 parts per billion. This was later reduced by the EPA to 80 ppb in 1998.

The position of the EPA is that scientific data proves that the benefits of chlorinating our water far outweigh the risks associated with THM's and other byproducts. While this can be considered a rational regulatory stance, there is insufficient data examining the safety of exposure to THM's on a daily basis over decades, and as a result questions it's strength. It is not whether THM's are carcinogenic, this has been established, but rather, is the average individual ingesting enough THM's through their drinking water for it to be considered a risk.  Unfortunately, our regulatory agencies have not addressed the interaction of chlorine and THM's once they enter the body. It is known fact that a weak carcinogen has the potential to be converted to a strong cancer causing agent by simply adding another weak carcinogen. As the human body is increasingly inundated with various forms of toxic chemicals and free radicals from the water, air, and food we ingest, you have to be left wondering whether the set risk intervals are appropriate given the untested myriad of interaction potentials.

On a positive note, the EPA is pursuing stricter standards for monitoring and addressing THM's. In a 2006 Texas EPA Public Drinking Water Stakeholder meeting focused on the health effects of disinfection byproducts(DPB), they state as a 2012 goal the following; "Intent of DBP2 [Disinfection ByProducts, Stage 2] – reduce the exposure of customers in areas of the distribution system with relatively high disinfection byproducts (finding the ‘hot spots’)", with operational objectives for municipality violations such as "Must evaluate distribution operations. Must describe plans to change things to fix things." and "Plans to minimize future exceeds."

How to Eliminate THM's and That Chlorine Smell!

To address potential long term health hazards, without falling prey to municipality distribution network inconsistencies and slow resolutions, the dependable solution lies in removing THM's at the point of use. You can reduce chlorination by-products by putting water in a jug and letting it sit in the refrigerator overnight, boiling water, or aerating drinking water in a blender. However, these tend to be unrealistic options for the everyday on-the-go person.

Home water filtration is a best fit, and one of the most effective methods for reducing THM's is through carbon and ceramic filters. A quality filter will remove that chlorine smell and taste, and also protect the small segment of the population that has chlorine allergies. A great choice is Berkey filters. They have the ability to remove Chlorine and THM's to undetectable levels and do so at a very low cost per gallon. Click here for a Berkey 101 Overview.

19 thoughts on “Chlorine in Our Drinking Water - A Cause For Concern”

  • Joseph

    Thanks for taking the time to go over and share this with us. I for starters seriously feel passionately about water filters and our health. I can tell that you have a very good amount of knowledge within the topic area, I would undoubtedly very much like to hear much more from you about this issue - I have bookmarked this website page and will be purchasing my berkey water filter soon.

  • Edmund Newingham

    Thank you for posting this great article on Chlorine. They've been chlorinating water in our town for as long as i can remember, and it stinks and tastes horrible. I bought a Big Berkey last month and my water tastes great again!!

  • Michael Miller

    chlorine in our drinking water has been a problem for a long time. i read the study on what it does to chickens when they drank chlorinated water and it was downright scary!!

  • Shreela

    How does Big Berkey affect chloramine?

    • Dan DeBaun

      Hi Shreela -

      At this point in time, the test results are not back on Chloramine removal. Given the filters use coconut shell charcoal as one of it's ingredients, the belief is that they will test well, as coconut shell charcoal is known to remove cholaramines.


  • Jon

    I'm wondering if the chloramine results are in yet? My city uses chloramine in the tap water.

  • gibby

    I just wanted to know if the test results for chloramine removal are in yet?

  • Steve

    Update, found this for anyone looking into this:


  • Stuart Tett

    Any update on the chloramine removal? I know all of the SF Bay Area (since California can now get Berkeys) and other communities would like a solution to this.

    If not is it still believed that Berkey will likely remove the chloramine?

  • Marc

    Do you have published testing on the removal of sodium hypochlorite ? My water company uses chlorine gas and sodium hypochlorite to chorinate our water supply. I am interested in removing both. Will the Black Berkey do it? THANKS.

    • Dan DeBaun

      Hi Mark -

      No, there is not specified testing, but below is information from the CDC on Sodium Hypochlorite,(http://www.cdc.gov/safewater/chlorination-faq.html), and how it shows up as free chlorine in minucipal water. The black berkeys have been tested for free chlorine and results are shown in the helpful resources section under "test results".

      7. If you add SH to water already treated in a municipal water treatment plant, is there a risk of a chlorine overdose?

      This is very unlikely. If sodium hypochlorite is added to water that is already treated, the water would most likely still be within an acceptable range of chlorine residual. Typically, chlorinated urban water systems have free chlorine levels of around 0.1 to 0.5 parts per million. We calculate our sodium hypochlorite solution dose to give untreated water a free chlorine level of around 1 part per million. So if you add our solution (to achieve 1 part per million) to treated urban water (0.1-0.5 parts per million), the level of the "overtreated" water would still be in the acceptable range of 0.5-2 parts per million (which is the range that balances disinfection efficacy and reasonable taste).

  • k

    have you tested for chloramine yet? whats the hold up?

    • Dan DeBaun

      Hi K -

      As with most of the testing delays we've experienced, the holdup is cost. The lab that was planning to do full through-end-of-life chloramine testing wanted 65k for the test. This is outside of the companies budget for just one contaminant, so they are working on locating a new lab.


      • tom

        your filters and systems cost much more than a normal carbon filtration system. all you would need to do is get a lab to test for chloramines in a sample from municipal water after filtration from the berkey elements. at least that would give us some info as to the filtering ability. chloramine is the main thing we are concerned about.

        • Dan DeBaun

          Hi Tom -

          Yes, the black berkeys do remove chloramines. More information on this testing here:



  • James Anderson

    Will your filters remove Bromine from spa water, if it becomes necessary to use as a source.

    • admin

      Hi James -

      The filters have not been tested for Bromine, so we do not know the effectiveness in ability to remove Bromine from the water.


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