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Chlorinated Water

By: Helena Stratford - Updated: 23 May 2017 | comments*Discuss
Chlorine Chlorinated Water Swimming

Chlorinated water has been around for the last 100 years or so, with its first recorded use as a water disinfectant being in 1897, when it was used to help control and reduce an outbreak of typhoid in Kent.

There is no disputing that chlorine performs a much-needed task as a water purifier, but do recent reports of associated health risks mean that its time to re-assess its impact on our health?

What Is Chlorinated Water?

Chlorinated water is water to which chlorine has been added in order to help purify it for human consumption. 90% of European homes receive chlorinated water with approximately 400 million glasses of it being drunk each day.

Why Is Chlorine Added To Water?

Chlorine is added to water either as sodium hypochlorite (bleach) or in the form of calcium hypochlorite (often added to swimming pools). Its used to disinfect water supplies due to its efficacy at killing harmful bacteria and pathogens, in helping to control the growth of algae and slime in water pipes and to help improve the odour and taste of drinking water.


While chlorine is able to prevent us from contracting many waterborne diseases such as swimmer’s ear or cholera and is thus a positive addition to water, it does have side effects which are currently attracting a lot of attention.

Trihalomethans or THMs, are volatile chemical compounds which form as a bi-product when chlorine is added to water and binds with organic matter already present.

Although the jury is still out on the harm that THMs might do, recent research has linked their presence in chlorinated water to the development of cancer and congenital birth defects.

The Absorption Of THMs

THMs are present in our water in different quantities across the country. Reports do vary a little, but levels can be as low as between 1 and 5 micrograms per litre and as high as 90. Approximately four million homes in Britain (that’s 1 in 6 households) are thought to have high concentrations.

The recommended maximum limit has been reduced from 100 micrograms per litre to 80 but stricter limits are being called for.

THMs can be absorbed into the body either by drinking or through the skin, so that taking a bath or shower, or going swimming is just as harmful.

Birth Defects

While there have been reports associating the consumption of THMs in water with an increased risk of cancer of the bladder, for the first time researchers have now also linked the compounds to the development of birth defects.

A report by Taiwanese researchers in conjunction with Birmingham University published findings that three specific defects could be caused by THMs – that of anencephalus, a brain deficiency, cleft palette, and hole in the heart. They stated that the risk for pregnant mothers was increased between 50 and 100 percent if they were exposed to quantities greater than 20 millionths of a gram per litre.

More Research Needed

More research is needed to analyse the effects of THMs on our health as the Drinking Water Inspectorate say that these findings are in contrast to their own studies which maintain that water containing THMs is safe for pregnant mothers to use.

However, most water companies agree that the findings can’t be ignored and that this is an area which will be revisited in months and years to come.

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