Water By Clara Lu — Date 01.31.2019

Water chlorination: Effective disinfectant or toxic additive?

Every day, millions of people around the world drink chlorinated tap water.

The treatment and distribution of water for consumption is considered a significant achievement of the last century. Disinfection, a chemical process whose objective is to control disease-causing microorganisms by killing or inactivating them, is unquestionably an important step in drinking water treatment.

By far, the most common method of disinfection in the United States is chlorination, employed in over 98% water supply systems. It does a marvelous job at eliminating most pathogens from the water we drink.

Before cities began routinely treating drinking water with chlorine (starting with Chicago and Jersey City in 1908), cholera, typhoid fever, dysentery, and hepatitis A killed thousands of Americans annually. Drinking water chlorination, among other purification processes at municipal treatment plants, has helped to virtually eliminate these diseases in the U.S and other developed nations.


Chlorine – The disinfectant of choice

Every day, approximately 170,000 U.S. public water systems treat and convey billions of gallons of water through almost one million miles of distribution system piping to individual households.

During the treatment process, chlorine is added to drinking water as elemental chlorine (chlorine gas), sodium hypochlorite solution, or dry calcium hypochlorite. When applied to water, each of these forms “free chlorine”, which destroys pathogenic organisms.

Chlorine is considered an almost ideal disinfectant based on its proven characteristics:

  • Effective against most known pathogens
  • Reduces many disagreeable taste and odors such as foul-smelling algae secretions and sulfides
  • Eliminates slime bacteria, molds, and algae that commonly grow in water supply reservoirs, on the walls of water mains, and in storage tanks
  • Provides a residual to prevent microbial re-growth and protect treated water throughout the distribution system
  • Suitable for a broad range of water quality conditions
  • Easily monitored and controlled
  • Reasonable cost


Protecting all the way to the tap

Frequently, slippery films of bacteria, known as biofilms, develop on the inside walls of distribution pipes and storage containers. Among disinfection techniques, chlorination is unique because only chlorine-based chemicals provide residual disinfection; they prevent microbial re-growth and help protect treated water throughout the distribution system.


The challenge of disinfection byproducts (DPBs)

When chlorine was first introduced to the water supply, it brought a rapid reduction in the spread of disease and other water-borne ailments. It made it easier for cities and towns to purify drinking water and to keep their residents safe.

Now, however, it seems like the use of this powerful chemical has a downside. While we recognize and applaud the benefits chlorine has brought us, it’s time we also become aware of the potential harms of having it in our drinking water.

When chlorine mixes with even minute amounts of organic compounds that are very often found in water, harmful byproducts – including chloroform – called Trihalomethanes (THMs) are produced. These byproducts produce free radicals in the body, which trigger cell damage, and are highly carcinogenic – even in small amounts.

As scientists look into the potentially dangerous effects of chlorine, use of the chemical has been linked to a wide range of ailments, including various cancers, reproductive problems, problems with the immune system, and heart attacks.

According to a report from the U.S. Council of Environmental Quality, the cancer risk for people who drink chlorinated water is up to 93% higher than for those whose water does not contain chlorine.

Other studies showing the harmful effects of consuming chlorine in water include:

  • According to research published in Environmental Health Perspectives, the by-products of chlorine are associated with an increased risk of bladder and rectal cancers.
  • A 2008 study based on an analysis of nearly 400,000 infants in Taiwan found that drinking water disinfected by chlorine while pregnant may increase the risk of having children with heart problems, cleft palate, or major brain defects.
  • According to a survey published in Annals of Allergy, Asthma and Immunology, chlorophenols, byproducts of water chlorination could be to blame for the rise in food allergies in the western world.

Chlorine plays an important role in protecting water from harmful pathogens. But when it isn’t removed properly, it can also do real harm to our health.


Bad taste and odor

Apart from health risks, chlorinated water also carries some odor and taste – the most obvious impact of its presence in drinking water. Yes, if your water tastes and smells chlorinated, it will be germ-free. But is that the quality of water most households want? As well as the chemical being present itself, dead microbes can remain in drinking water once the chlorine has destroyed them, which can also cause an unpleasant taste.


The future of chlorine disinfection

Despite these issues, chlorination will remain a cornerstone of waterborne disease prevention. A report published by the International Programme on Chemical Safety stated: Disinfection is unquestionably the most important step in the treatment of water for drinking water supplies. The microbial quality of drinking water should not be compromised because of concern over the potential long-term effects of disinfectants and DPBs. The risk of illness and death resulting from exposure to pathogens in drinking water is very much greater than the risks from disinfectants and DBPs.

While there are regulatory limits for THMs and residual disinfection levels in place, and water treatment plants have adopted methods to reduce DBP formation, it is still better to err on the side of caution.

The most low-tech solution is to fill a carafe with tap water, and let it sit in the refrigerator for 24 hours, during which the chlorine will evaporate. You can also boil the water to remove chlorine. These two solutions will get rid of most of the chlorine, but can also be inconvenient and leave other pathogens behind. The best solution is to invest in a quality water treatment system for your household.

At Mitte, we understand the challenges involved in attaining not just pure, but also healthy water* in this day and age. After two years of R&D, prototyping, conducting experiments and user testings, we have built a machine that both purifies and enhances your drinking water. Inspired by the natural water cycle, it first purifies tap water with a proprietary distillation-based method, then enhances that pure water with essential minerals.

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