Trouble with chlorinated water

By EDUARDO GONZALES, MD

April 26, 2011, 10:30am

Q: We recently got connected to Maynilad. After many years of buying dirty water from delivery trucks, we finally have potable water coming out off our faucets. I know Maynilad water is potable, but does it not contain chlorine? I think I read somewhere that drinking chlorinated water carries some health risks? Is this true? --Enrico P., Las Pinas City

A: Yes, Maynilad chlorinates water as part of its process for making its water potable. Chlorine is perhaps the most commonly used disinfectant worldwide. At its usual concentration in drinking water (two to three parts per million), chlorine is very effective in killing most disease-causing or pathogenic microorganisms—bacteria, viruses and parasites including protozoa—except for a few hardy species (e.g., the protozoa cryptosporidium).

Up to now, most public health experts still say that chlorination of water intended for human consumption is the cheapest, most effective and safest way to prevent life-threatening waterborne diseases such as cholera, typhoid fever and amebiasis. Indeed, chlorination of drinking water, which started early this century, has been regarded as one of the greatest advances in public health ever.

Aside from destroying pathogens, chlorine has other benefits. It controls the growth of microorganisms, fungi and algae in water reservoirs and pipes, and in the process, it keeps water pipes patent. It likewise neutralizes the taste and odor of algae and decaying vegetation, making drinking water more palatable. It also eliminates obnoxious gases and compounds like ammonia and hydrogen sulfide from water.

But you are right. Drinking chlorinated water carries some health risks. Chlorination of drinking water has been previously regarded as completely safe, but recent scientific evidence proves otherwise. For example, some epidemiologic studies have indicated that long-term (i.e., 15 years or more) drinking of chlorinated water increases the risk of developing cancer of the colon and urinary bladder.

Actually, it is not chlorine, per se, that is hazardous to health. Rather, it is the by-products that are generated by the chlorination process. Chlorination by-products, often referred to as disinfection by-products (DPBs), are chemical substances that are produced when chlorine reacts with certain organic substances in water during the disinfection process. There are several kinds of these chemicals but the most studied are the trihalomethanes of which the most prevalent is chloroform. Other common DPBs are bromodichloromethane, chlorodibromomethane, bromoform, chloroacetic acid, trichloroacetic acid and dichloroacetonitrile.

In animal experiments that employ mostly rats and mice, chloroform has been shown to produce liver and kidney tumors; while the other DPBs have been variously associated with liver and kidney tumors and damage,  tumors of the intestines, damage to the nervous system and some reproductive abnormalities.

Incidentally, the animal experiments on DPBs used doses that are much higher than those present in drinking water. Also, the mechanism of tumor formation in mice and rats are considerably different from that in humans. Nevertheless, the potential health hazard arising from DPBs in humans can’t simply be written off.

Despite the apparent health hazards that accompany chlorination of drinking water however, to discontinue this practice would be foolhardy, at least until an equally effective and cheap, yet safer, alternative process has been developed.

At present, there are substances and devices available in the market that can remove DPBs or the organic substances that serve as precursor of DPBs from chlorinated drinking water. One of the cheapest among these is activated carbon which removes chloroform and other DPBs. Thus, if you filter your tap water with a device or filter that contains activated carbon, this will surely reduce your health risks from DPBs.

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