MadSci Network: Environment & Ecology

Re: Is chlorine in our tap water good or bad?

Date: Sun Oct 26 17:15:43 2003
Posted By: Peter Gaul, Grad student, OHS & Environmental Management, company - non educational
Area of science: Environment & Ecology
ID: 1067188757.En

That's a very clever question Christine and one that, as you have found 
out by searching yourself, is not so easily answered.  Experts all over 
the world claim both sides of the argument.

In its natural form Chlorine is a Yellow-Green gas that is released from 
volcanoes and is deadly.  However it is mostly used by people in 
compounds (this is when it is linked to other chemicals) such as bleach 
that your parents use to clean the floor or bathroom through to the salt 
that you put on your food.  You can see from these examples that chlorine 
can be deadly, through somewhat poisonous right down to totally safe. - 
See http://www.aaawatertest

The chlorine in your drinking water is used like the bleach you use on 
your floor in that it is designed to kill micro-organisms.  In this case, 
the ones that are living naturally in water, but can cause sickness and 
disease in people - particularly when in large numbers.  Therefore the 
chlorine added to the water is obviously poisonous - designed to kill.

In Sydney Australia in 1998 our water was polluted with high 
concentrations of Giardia (parasite that is the most common cause of non-
bacteria diarrhoea in North America) and Cryptosporidium (parasite that 
is passed through faeces) despite having chlorinated water.  The result 
was that many people became violently sick and we were forced to go back 
to boiling their water.  Sydney Water now strictly test and report on 
these micro-organisms - See the daily reporting at
Learn more about "Bad Bugs" at

While chlorination can't guarantee to kill each and every nasty in the 
water it is currently one of the best ways of doing the job.

Despite being poisonous, the good news about the chlorine added to your 
water is that it is strictly controlled in the western world.  The other 
thing to take into account is that the compounds of chlorine added are 
very unstable.  This means that they naturally break down and change form 
releasing the chlorine.  Due to this it is likely that by the time you 
are drinking the glass of water it will contain little to no chlorine.  
Unfortunately it can still contain some other chemicals - Find out more 
at http://www.aaawatertest

Despite all this I, like you, am still concerned about drinking chemicals 
that I can easily remove.  I therefore drink filtered water but will make 
an effort to drink some tap water throughout the week - for the benefits 
of fluoride to my teeth and to ensure that my immune system is exposed to 
some of the micro-organisms that survive the chlorination process.

I guess my answer is as unclear as others you have read.  So here's the 

1) Water naturally contains many chemicals and potentially harmful micro-

2) Chemicals are added to drinking water in developed countries in the 
interest of our health - chlorine to kill micro-organisms, fluoride for 
your teeth (fluoride is another chemical that that many scientists are 
now saying is not safe).

3) The chemicals that are added are strictly measured.  Chemicals already 
present (naturally) are strictly tested, as are bacteria and other micro-

4) The use of these chemicals has shown tremendous benefits in health in 
the countries that add them.

5) Studies show a slight increase in the incidents of colon, bladder, 
rectal (all organs used in the digestion and transport of water in your 
body) cancer in people who drink chlorinated water.

So it's a matter of weighing up the risks with the benefits.  In the 
meantime be sceptical about "the best invention in history" claims 
because the pesticide DDT was also labelled like this, as was CFCs in 
spray cans along with many other chemical inventions that were later 
found to be very damaging to people and/or the environment.

For other non-chlorination ways of water purifying go to and ask
"how many ways are there to purify water".  You'll see that chlorine may 
be the only way to mass-process water cheaply at the moment but there are 
other ways at home or camping.  

Time is the true test of what is a good invention - along with lots of 
research along the way.  Maybe you can tell your grandkids what you think 
about Chlorine in 45 yrs when a better way is being used.

Current Queue | Current Queue for Environment & Ecology | Environment & Ecology archives

Try the links in the MadSci Library for more information on Environment & Ecology.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2003. All rights reserved.