Drinking water – or bathing in it – can be deadly (not)

One of the staples of the Alt Health world is to convince people that all sorts of rather commonplace things are, in fact, bad for you.

The scariest is if something “increase your risk of cancer”. Although heart disease kills more people, cancer tops the list of the diseases people are most scared of, and the mention that something “increases cancer risk” is a sure-fire scary scare.

Once you have your marks, sorry, patients, scared, and doubting the safety of hitherto commonplace and unscary things, then the Magisterial Authority of the Nutritional Expert, or Holistic Practitioner, will give them something to cling to. And pay for.

Resulting, of course, in a pronounced lightening of the “patient’s” wallet.

If you work it really well, the people are so grateful that they never realise they have been sold the cure to a non-existent illness.

So let’s move on to the actual scares. Many of the lines Alt practitioners use to make people nervous, and foster the belief that “everything is bad for you”, are actually flat-out nonsense – the farrago over mercury in vaccines and autism being one famous (or infamous) example. However, sometimes the Alties’ lines may be based on at least a grain of evidence.

Should this, then, convince you that you have been lied to by the mainstream, and that the Alties are revealing important truths that were kept from us?

Well, not necessarily.

The statement may be true, but it is important? Or, to put it more scientifically, Is it significant?

The Devil, as they say, is in the detail.


Something nasty in the water…

Let’s discuss a real example.

Dr John Briffa is a medical doctor and a well-known writer about nutritional topics in the UK, both in the media and via his blog at www.drbriffa.com/. For some years now, Briffa has been telling his readers that they should drink bottled water rather than tap water. His stated reason is (taken from a recent post on his blog):

“…there is quite a body of evidence linking the consumption of tap water with an increased risk of cancer” [1]

and from a few years back, when he wrote an Observer column:

“The sanitation of tap water taints it with chlorine and by-products of the chlorination process that have toxic potential. Studies have linked the consumption of tap water with an increased risk of certain cancers (such as those of the bladder and rectum).” [2]

Now this second statement is more accurate, and adds some information – here you are told what cancers, not just “cancer”. But still, on its face, this sounds really scary. I suspect a certain fraction of the people that read this, particularly those least scientifically and medically literate, will see this as:


“Don’t drink tap water – it will give you cancer”


When Briffa repeated the “avoid tap water” comment on his blog recently, one reader asked him to give the evidence to back up the statement about cancer risk. In response Briffa reproduced the abstracts of several scientific studies and meta-analyses (see comment 3. in the thread at Briffa’s blog, [1]). There was no explanation of what the studies meant, and no context – see below – but they were real enough, published in proper scientific and medical journals.

So there is evidence to back it up! It’s true! Tap water increases your cancer risk!

Well – yes, and no.

The increase in risk is consistent between studies. Indeed, it is sufficiently well recognised that some mainstream health sites dealing with bladder cancer repeat it. For instance, the Cancer Research UK site says quite plainly:

“Drinking chlorinated water (water with chlorine added) may cause a small increase in bladder cancer risk compared to water disinfected in other ways.” [4] [Emphasis mine]


– Note that this means this can hardly be: “A terrible secret they tried to keep from you” – more “something that might be true, although we’re not sure, and with the causation not settled, and viewed on balance as an acceptable risk, as well as not being easily avoidable”. We should remember here that 120-odd years ago, before we had safe drinking water, bacterially contaminated water regularly used to cause epidemics of nasty diseases like cholera and kill loads of people. This is still true in large parts of the developing world, as you can read here.



Context, context, context

SO… what is the snag with the statement as presented on John Briffa’s blog?

To my way of thinking, the problem is the lack of explanation, and particularly of context. The basic statement “there is quite a body of evidence linking the consumption of tap water with an increased risk of cancer” leaves out several crucial pieces of information that you need to put this information in context.


– It doesn’t tell you how common the cancers for which this has been shown actually are;

– It doesn’t tell you how much the chlorinated water is said to increase the risk;

– It doesn’t tell you if we know for certain that drinking the stuff causes the increased risk, as opposed to, say, bathing in it;

– It doesn’t tell you how well the studies eliminated possible “confounding factors” – for instance, if all the people drinking chlorinated water lived in polluted cities, while those drinking artesian non-zapped water lived healthy lives in the country.

– It never makes the basic point that it is notoriously difficult to infer causation from epidemiological studies of this kind, partly because of the confounding factors. A famous saying is “correlation is not causation”


– It doesn’t tell you that all sorts of other things will slightly increase, or decrease, your risk of these kinds of cancer.

[This last one is the source of numerous black jokes in science about everything in the world either increasing, or decreasing, your risk of cancer. Sometimes the same thing increases the risk of some cancers and decreases the risks of others. Swings and roundabouts.]



Anyway, without this kind of information, which you are not given by being told “There is scientific evidence that cholorinated water increase cancer risk” you cannot make a sensible judgement about whether to be worried.

Instead, you just worry. And then drive off to the supermarket in your 4×4 SUV to get a huge multi-pack of bottled mineral water. Ker-chhhinnng.

So what is the truth about chlorinated tap water and cancer risk? If I was putting in the context, I would state it roughly as follows:


“In studies, people who drinking chlorinated tap water all their lives seem to have a very small increased risk of bladder cancer – about 20% – and perhaps of rectal cancer too. However, we are still not totally sure this is due to the chlorinated water, and not to something else that is different about the groups of people, like maybe the ones who drink bottled water simply drinking more than the ones who drink tap water. And even if we accept the idea that it is really the chlorinated water that does it, we don’t know for sure whether the risk is due to drinking the water, or bathing and swimming in it – probably both. And you have to drink or bath in the stuff for at least 35 years to get this 20% increase in risk. There is no suggestion chlorinated water increases the risk of other kinds of cancer, including those which are far more common than bladder cancer, like lung cancer and prostate cancer.

It is also important to remember that risk factors do not actually tell you if you are going to get a disease. Most people who have all the risk factors still don’t get the disease. And conversely, some people who have no risk factors do get the disease.

Next, even if we accept the “chlorinated water hypothesis”, the increased risk of bladder cancer from drinking chlorinated water is probably considerably LESS than the increased risk of this cancer you seem to have if you don’t eat the recommended five daily portions of fruit and veg. It is definitely far, far less than the increased risk of this cancer that you have if you are a smoker (which doubles or triples the risk – smoking is thought to account for about 50% of all bladder cancer cases). And if you are a non-smoking man, simply being male is your main “risk factor” for bladder cancer (it is three times more common in men). (For the source of the relative risk figures, see [4])

Bladder cancer, by the way, is usually diagnosed when you are past 70, and is one of the more treatable cancers. You are statistically about as likely to die of bladder cancer as you are to be killed in a road accident. You are about twenty times MORE likely to die from heart disease, eight times more likely to die from a stroke, and about three times more likely to die of prostate cancer.

PS Finally, to retain a sense of proportion, it is also necessary to bear in mind that life has a 100% mortality rate, so something is definitely going to get you in the end.”

I didn’t know about the chlorinated water / bladder cancer work, so it came as a slight surprise when I heard about it from one of Briffa’s readers. However, having looked it up, I will not be giving up drinking chlorinated tap water.

What I dislike about John Briffa’s way of presenting this, as will by now be apparent, is the lack of context. Another example – no absolute risk figures. Bladder cancer is not a rare cancer – in Europe it is about the 5th most common cancer overall– but that still doesn’t make it common, in the sense most people fear, namely “you are quite likely to get this and die of it before your time”.

Because so many things alter the risk, it is hard to give a precise number for “how likely is it I might get bladder cancer” As a ballpark, as a non-smoking man eating a reasonably healthy diet, your risk of getting it by the time you are 70 would seem to be in the order of 1 in 200 at the most. As I have said, there are many other diseases you should be far more worried about. A marginally increased relative risk of 20% for one particular kind of cancer, or even two kinds if one adds rectal cancer, is not going to keep me awake at night.

ESPECIALLY since, even were I to decide to stop DRINKING chlorinated tap water, I am not in a position to stop BATHING in it, which probably accounts for 2/3 of your total “chlorination byproduct exposure”. Mrs Dr Aust wouldn’t stand for the not washing, even if I could.

So, much as I would like to say:

Avoid increased cancer risk – DON’T WASH! EVER!”

…I shall refrain.


Let’s INVERT that risk factor

Risk factors are interesting. They are the meat and drink of medical and scientific papers about causes of disease, but are notoriously poorly understood. And peoples’ reaction to them is quite strange and unpredictable. The same “risk rate” means different things to people in different contexts.

An interesting way to probe how you view a “risk factor”, I find, is to “invert” it – to turn it back to front. This is because “increase” always sounds more scary, and hence more useful to someone trying to sales-pitch you, than “decrease”

Thus, instead of saying “XYZ increases your risk of ABC cancer by a fifth” (itself an advance on just saying “XYZ increases your cancer risk”, but still scary-sounding because it has “Increases” – MORE cancer, hence frightening), try inverting this to:

“Did you know that if you stopped doing XYZ you could reduce your risk of ABC cancer by an Nth?”

That way it avoids sounding scary (no “increase”) and also the focus tends to be on the XYZ, the behaviour, rather than the scary stuff. I would argue this means you can consider the risks in a more sensible “cost-benefit” way, rather than through a prism of “primal fear of nasty disease”.

Let’s take a real example:

“Do you know you can reduce your risk of bladder cancer by about one-sixth if you never drink, or bathe in, or swim in, chlorinated water?”

[Note again that this accepts the relationship as “causation proven”, which it isn’t]

Presented with it that way, I would bet money that most people, for whom bathing in asses’ milk or Evian water is financially out of reach, and who don’t have a Malibu Colony beach house with a solar-heated sea water shower, would probably not be that bothered.

Which seems rational to me. Because by living – not to mention eating, and drinking, and walking and sleeping, and driving a car – you are accepting some intrinsic risks. C’est la vie – literally.


More risks in context

It turns out that reading about bladder cancer is a smorgasbord of interesting papers about risk. Here is another example. Studies report that you actually seem to have an increased risk of bladder cancer if you are a lorry driver – strange but true. In fact, the reported increased risk of bladder cancer for spending a lifetime drinking and abluting with chlorinated tap water (around 20% in several studies) is a little more than the risk increase if you drive a lorry (about 17%), but a bit less than if you drive a bus (33%) [5].

Again, I find it difficult to imagine many lorry or bus drivers quitting on account of this, even if they all knew. They have a living to make, so they will probably accept the marginally increased risk – if they care at all.

So to reiterate: with risk, it seems to me, you need to ask whether we are reasonably sure about the causation; you need accurate numbers, preferably absolute ones, rather than relative risk increases; and you need context. Only then can you think sensibly about whether the risk is a real concern, perhaps enough to want to change your behaviour. On which basis, there some health-risking behaviours that are self-evidently worth avoiding, if you possibly can. Smoking is one. Being grossly overweight is another.

But as for avoiding drinking water out of the tap – give me a break.

My advice: save yourself some money, and a ton of empty plastic bottles.

[1] http://www.drbriffa.com/blog/2007/12/31/chief-scientist-of-fsa-discredits-detox-regimes-without-using-any-err-science/

[2] http://observer.guardian.co.uk/magazine/story/0,,1276931,00.html

[3] http://www.cancerhelp.org.uk/help/default.asp?page=2695

[4] Murta-Nascimento C et al. (2007). Epidemiology of urinary bladder cancer: from tumor development to patient’s death. World J Urol 25: 285-95. PMID: 17530260.

[5] Boffetta P, Silverman MT (2001). A meta-analysis of bladder cancer and diesel exhaust exposure. Epidemiology Jan;12(1):125-30. PMID: 11138807


20 Responses to “Drinking water – or bathing in it – can be deadly (not)”

  1. jdc Says:

    Good stuff Dr Aust. I enjoyed reading that.

    Re “So, much as I would like to say: “Avoid increased cancer risk – DON’T WASH! EVER!” …I shall refrain.” – the Daily Mail, of course, has a piece online titled “Chlorine in the bathwater is linked to cancer” here: Daily Mail on Chlorine

  2. dvnutrix Says:

    :Applause: Well done, Dr Aust. Sums up the dissembling around this topic and the lack of any meaningful context. I got a lot out of your risk comparisons.

  3. lsnduck Says:

    That was a well put together and easy to read piece, thank you. The general principles are well worth considering, particularly the ‘inverting the risk’ exercise.

    On the specific topic discussed, I think it is well worth reiterating the dangers of water that unclean water bring. The possible risk from chlorine is massively outweighed by the risks of water borne disease.

  4. dvnutrix Says:

    Orac has covered water woo today – at one point, I thought we were going to be told that we could save vast amounts of the usual costs of water-processing by dragooning infants from the local schools to hold hands around the storage tanks and sing Kumbayah – sadly, not. It seems chlorine is cheaper, more effective and safer.

  5. LeeT Says:

    Thanks for that. You have put the studies in context. They say get a second opinion if you are not happy with your “Dr”!

    Most people I know seem to drink tap water so any study of drinkers of bottled water would probably be a very small section of the population.

  6. Dr Aust Says:

    Hi Lee

    The more recent studies, like the one referred to in the Peoples’ Medical Journal, sorry, I mean the Daily Mail, that JDc linked to above, try to do the epidemiology in a much more sophisticated way, mostly by asking people how much they drink daily, what fluids they drink, what water they used to make drinks, how often they bathe, for how long etc etc. They also try and match the locations to remove the possible confounding “geographical factors”, and match as many of the other risk factors as they can. But it is notioiously difficult to eliminate all confounding factors, as you may not know them… and also the risk increases being measured here are small.

    The deeper B/G to this, as you will know having read Briffa’s blog, is the Nutri-gang’s mantra of “Eight glasses a day!” “Keep sipping!”…

    …and then adding, once the people are swilling down far more water per day than they actually need: “Oh no, but not tap water, it’s chlorinated…!”

    Result: bottled water manufacturers make money, Alt health outfits selling fancy water filter systems make money, supermarkets make money selling bottled water and water filters, nervous punters think Nutritionistas are founts of wisdom, buy books, buy supplements etc etc.

    Incidentally, it is a little appreciated fact that some cheaper bottled waters are made with … chlorinated municipal water. Who’d have thought it?

  7. Sili Says:

    Interesting – if it really was the chlorine, I’d expect swimmers to have a higher risk. But of course they’re likely fitter than non-swimmers, so the comparison would have to be between pool and ocean. swimmers.

    (As an aside – Danish water is never treated in any way. We have ridiculously low limits on what can be in the water – they’re essentially arbitrary; put at the detection limit of the available aparatusses at the time the legislation was passed – and even private boreholes aren’t allowed to purify with active carbon.)

    What amuses me is that the media (here at least) are very upset about plasticisers and softners too — the kind used in making bottles for instance.

    And that doesn’t even touch upon the particular pollution and GHG emissions from carting all that water about.

  8. nthnlsmmrs Says:

    It really does seem like just about everything increases the risk for some sort of cancer. Personally, I got tired of hearing it all years ago and haven’t paid any attention to a lick of it since. You are totally right, all the studies seem to be taken out of context. Eat right, exercise, die anyway.

  9. gimpy Says:

    Excellent article but I have to say that as a fish owner chlorinated water is a bugger. It means you have to buy ridiculously overpriced water treatment solutions from aquarium shops (or syphon it off from xenopus and zebrafish labs). Are the municipal authorities in league with big fisha?

  10. draust Says:

    I have the same problem with Daphnia (waterfleas), Gimpy (too complicated to explain), though obviously there the quantities of water required are less.

    Of course the fact that aquarium fish don’t like chlorinated water will merely confirm the water-nuts in their paranoia. Explaining the scientific differences – fish are in water all the time, and are continuously passing water over the gills and drinking, none of which are true of us -doesn’t seem to work. Ah well.

  11. Alan Says:

    You can always just aerate the water for your aquarium overnight and most of the chlorine will be driven off. Unless your council use chloramine… in which case you will need a bottle of magic solution from the fish shop.

  12. draust Says:

    Thanks Alan, good tip. The deionized / distilled stuff at work does the trick, but lugging it home would certainly be a pain.

    So far I have resisted having a fish tank at home because:

    (i) last time I kept tropical fish in my distant youth they all ate one another (v. Darwinian);
    (ii) Mrs Dr Aust wouldn’t stand for it;
    (iii) Jr Aust would probably frighten the fish to death.

    I’m thinking of instituting a Danio tank in my office, though. It would be good for my mid-life stress. Now all I have to do is bribe, I mean, square it with, the safety guy…

  13. Claire Says:

    “Eat right, exercise, die anyway”

    excellent! but unfortunately not a slogan designed to boost sales of diet plans, supplements, consultations with nutritionists, lifestyle magazines…

  14. Lindy Says:

    Well, just to throw another spanner in the works, how about microwaved water? This link

    Click to access MicrowavedWater-SeeWhatItDoes2.pdf

    tells you all about it. The guy clearly has a mission and a little girl’s school experiment confirms everything, including the fact that microwaved food causes brain damage – permanent too!

    Goodness knows what happens if you use chlorinated AND microwaved water. Please be careful everyone.

  15. What could be so fine… as to be alkaline (Warning: Irony) « Dr Aust’s Spleen Says:

    […] Part 1: Drinking water – or bathing in it – can be deadly (not) […]

  16. camwoo Says:

    I like the post, although it may be a bit late to reply.

    Still, re statement in nearly last paragraph: “On which basis, there some health-risking behaviours that are self-evidently worth avoiding, if you possibly can. Smoking is one. Being grossly overweight is another” – you may find you wish to reconsider this last statement after reading the excellently researched articles by Ms Sandy Szwarc on her website junkfoodscience.blogspot.com, which debunks obesity and food-related health scares, among other things.

  17. Water Treatment Says:

    >> Excellent article but I have to say that as a fish owner chlorinated water is a bugger. It means you have to buy ridiculously overpriced water treatment solutions from aquarium shops (or syphon it off from xenopus and zebrafish labs).

    There are some other methods besides chlorination on purifying water and making it pure drinking filtered water.

  18. hi thar Says:

    The problem isn’t really with chlorinating water (like pool water), it’s in chlorinating water that’s full of organic compounds (say, because it came from a lake). This creates known carcinogens. Thus it’s a bit depressing (but not at all surprising) to find out that epidemiological studies confirm that the carcinogens increase the risk of certain cancers.

    That said, I just put a filter on my tap and hope for the best. There’s really no regulation on bottled water in the US so it can seriously come from anywhere, plus it’s awful for the environment. Add the waste of all those bottles to the distortion of the fresh water system that happens when a bottler decides a certain stream is lucrative or tasty and gets the damnfool local water board to give them permission to suck it dry. Water boards are supposed to be managing the water supply for the locals, not for the sake of commerce.

  19. Benjamin Frankin Says:

    Substantially, the article is in reality the freshest on this worthw hile topic. I agree with your conclusions and will thirstily look forward to your upcoming updates. Saying thanks will not just be enough, for the wonderful clarity in your writing. I will directly grab your rss feed to stay privy of any updates. Good work and much success in your business endeavors!

  20. Debbie Rogers Says:

    I have an 9yr old daughter and we have well water that is not softened or filtered. How often should she bathe? I have been having her bathe with my assistance every three days, is that ok?

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