The Night I Bought a Water Filter

Joe Schwarcz, Ph.D.
December 2, 2001

It was a dark and stormy night. Really. There was a knock at the door. The well-dressed gentleman on my doorstep introduced himself and proceeded to ask me a rhetorical question: “Are you interested in good health?” For a moment I pondered putting an end to the encounter by saying, “No, I would rather be cold, hungry, and sick,” but I thought better of it. Why not let him have his say? I invited him in.

“I notice you have a tap in the kitchen,” he began, quickly demonstrating his keen powers of observation. I admitted that we had, indeed, opted for a house with indoor plumbing, despite the health benefits we might have attained by carrying buckets of well water during the Canadian winter. “You don’t actually drink that water, do you?” he went on. As if admitting to a crime, I replied that not only did we drink the tap water, but we also gave it to the cat. This seemed to cause the man grave concern: “It has chemicals in it, you know.” I think he was a little taken aback that this bombshell didn’t immediately cause me to clutch my throat; he evidently decided that heavier artillery was needed. “Invisible chemicals,” he explained. By now I had a pretty good idea where he was going with this, but the time was not yet ripe for a lecture on why “chemical” isn’t a four-letter word.

“Would you like to see those invisible chemicals?” he asked. Before I had a chance to ask how anything invisible could be seen, he began unpacking some equipment from his briefcase. The equipment looked impressive. It turned out to be some sort of electrical device fitted with a pair of metal rods that looked like electrodes. Next he asked for a glass of water from my tap. He sniffed it, and, apparently convinced that the liquid was sufficiently toxic, proceeded to immerse the electrodes in it. Then, with a cry of “Watch this!” he plugged the device into a wall socket. Within 30 seconds the water started to turn cloudy, and within a minute it had formed a repulsive yellow scum. “You see!” the man cried triumphantly, implying that by passing an electrical current through the water he had scared those nasty chemicals out of solution. The toxIns had been comfortably dissolved, it seems, until the fear of being electrocuted prompted a mass exodus.

Then came the coup de grâce. He extracted a water filter from his bag and attached it to the tap. He proceeded to subject the filtered water to the same kind of electrocution as had been experienced by my “toxin-laden” tap water, but this time the results were dramatically different. There was no yellow sludge, because those invisible, noxious chemicals had been “filtered out.” Surely, the couple of hundred dollars this miraculous filter cost was a small price to pay for my family’s health. But if I was still unconvinced, the salesman told me, he had lots of documentation to support his claims. Out came newspaper clippings about the various dangers that lurked in tap water, including expert testimony on how chlorine had been used as a poison gas during World War I. Again he reached into his bag. I waited for him to pull out a gas mask — I’d been wondering how he had dared to confront a lethal water tap without suitable protection in the first place. But no, instead of a gas mask, he grabbed a bottle of ortho-tolidine. He informed me that this substance would reveal the presence of chlorine in water by turning yellow. Sure enough, my tap water contained chlorine.

Now the man asked me to place a couple of fingers in a fresh glass of tap water and wait a few minutes. He tested the water again with ortho-tolidine, and this time there was no telltale yellow color. The toxic chlorine, he insisted, had been absorbed into my body. Exactly the same process occurred, I was told, every time I took a shower. No need to give up showers, though: the filtered water had no chlorine residue, and he had a filter that would fit any shower. With this dramatic demo, my lesson in toxicology and chemistry came to an end.

It wasn’t easy, but I bit my tongue and made it all the way through. I didn’t even react when the salesman talked about “soaring cancer rates,” “bodies overburdened with toxins,” and “scientists brewing up deadly chemical mixes.” I resisted pointing out that the average life expectancy lengthens every year and that while some cancers are increasing, others are declining. I didn’t even mention that the introduction of water chlorination was probably the greatest public health advance in history. But now it was my turn. Time for me to give a little chemistry lesson.

I began by picking up the glass of yellowed, scummy tap water, the one in which those nasty chemicals were no longer invisible, and raising it to my lips. Before the salesman had a chance to stop what must have seemed like a suicide attempt, I downed the contents. At this point the poor man’s face turned the color of the liquid in the glass. He must have thought I was mad. But I knew that I wasn’t taking any risks; I’d figured out what was happening. The yellow sludge wasn’t coming from invisible chemicals that had been jolted out of solution. It was coming from one of the electrodes. Electrolysis is a commonly performed chemical procedure in which two electrodes are immersed in water and a current is passed between them. This causes water to break down into oxygen and hydrogen. But if one of the electrodes is made of iron, it reacts with water to form a precipitate of yellow iron hydroxide — or rust.

So, all I was doing was drinking a little rust, just a form of iron supplement, I explained to the incredulous salesman. I decided to punctuate my little performance by taking his glass of filtered water, adding a few grains of salt, and subjecting it to a current. Within seconds the familiar yellow scum formed. The salesman watched in awe. What kind of a magician was I? He was confused. I explained to him that water conducts electricity only when it has ions dissolved in it, and his filter had removed these ions. Therefore, no scum. But when I added a little salt, electricity flowed through the water and allowed the iron electrode to rust. To prove my point, I replaced the iron electrode with an aluminum one and invited him to torture my tap water with his apparatus once again. Since this time he used no iron electrode, there was no scum.

Next we tackled the chlorine problem. I drew two glasses of tap water and placed them on the table. I inserted a couple of fingers in one and asked the salesman to hold the other. A few minutes later we tested each for chlorine content. Neither glass had any. Chlorine, I explained, evaporates. It goes into the air, not into the skin. I wasn’t sure how effective my arguments and demonstrations had been. The salesman pointed out that the scum had formed with tap water and not with filtered water, so the filter had done something. I couldn’t argue with that logic.

Certainly, this was not the only occasion that I’d found myself listening to curious chemical stories and bewildering claims. The business of bringing science to the public through books, newspapers, radio, and television tends to prompt requests for consultations. Over the last 20 years or so, an assortment of entrepreneurs has visited me at home or at my office either to solicit my opinion on a product or to entice me into a “can’t lose” business venture based on some miraculous cure-all. I’ve seen and heard everything: crystals, magnets, pyramids, countless dietary supplements, convoluted weight-reduction schemes, special oils, oxygenated liquids, deoxygenated liquids, odor removers, odor-producers, exotic juices, ionizing bracelets, herbal concoctions, antioxidants of every description, parasite-killers, therapeutic glasses, foot deodorants, water magnetizers, blankets that heal, and charcoal-laden underwear that counters the effects of bean consumption.

By and large, the people I’ve met, and continue to meet, are well meaning and not out to defraud others. But they do share an unrealistic and overly simplistic view of the way the world works. They recklessly bandy about terms like “toxIns,” “chemicals,” and “poison” while misguidedly revering “natural” substances. Most possess only the vaguest understanding of molecules, chemical reactions, and research methods. They have little appreciation of the power of the placebo or the confusion that can be created by undue reliance on anecdotal evidence. True, science does not have all the answers and scientists do make mistakes, but sticking to the scientific method is still our best shot at progress.

Much of my professional work attempts to demystify science — to provide a few scientific glimpses into the workings of our complex world. I hope that by offering explanations for a variety of common phenomena, I can help others understand how the scientific method functions and, at the same time, lay down a solid foundation for critical thinking.

That, of course, was just what I had in mind as I met with the water-filter salesman. I could lead him to water, but could I make him drink it? My demos and explanations may have had some effect, because when I offered him a cup of coffee, he happily sipped it, despite the fact that it had been brewed with water from my tap. It was then that I decided I had tormented the poor soul enough and that I should reward him for sitting through my chemistry lecture. He just about fell off his chair when I said I would buy a filter. Of course, my decision had nothing to do with his irrelevant demonstrations. I had been contemplating purchasing a filter, anyway. These devices do remove a number of undesirable substances that escape municipal treatment — trihalomethanes, for one. While chlorine unquestionably saves millions of lives by killing bacteria that can cause disease, we do pay a small price for using it. Chlorine reacts with some dissolved organic compounds to produce trihalomethanes, which are carcinogenic. Activated carbon filters remove these, as well as a variety of other pollutants. U.S. and Canadian water-quality standards call for limiting trihalomethanes to 100 parts per billion (ppb). Whereas the risk of drinking tap water is very small compared with other risks we face, it is easily reduced by using (and properly maintaining) a good filter. In addition, I believe that water tastes better when it is free of chlorine residues.

So, I wrote a check for the filter, gave my new friend a chemistry text, and hoped that he would reap some benefit from our visit. The night, I thought, had been dark and stormy for him in more ways than one. I watched through the window as he braved the weather and headed towards the next house. The the man who was so worried about the chemicals in my tap water paused for a moment, reached into his pocket, pulled out a cigarette, and lit up.

For Additional Information


Dr. Schwarcz is director of McGill University’s Office for Chemistry and Society. In addition to teaching chemistry at McGill, he hosts a weekly “phone-in” show about chemistry on Montreal radio station CJAD, writes a weekly column called “The Right Chemistry” in the Montreal Gazette, and has a regular TV feature entitled “Joe’s Chemistry Set” on the Canadian Discovery Channel. This article was adapted from the preface to his book The Genie in the Bottle, a collection of commentaries on the fascinating chemistry of everyday life.

Quackwatch Home Page

This article was revised on December 2, 2001.