Interdisciplinary Minor in Global Sustainability
Senior Seminar (Instructor: Peter A. Bowler)
University of California, Irvine, April 1998

Rethinking Chlorinated Tap Water

By Daniel G. Nunez

With the aggregation of millions of people in large urban centers, there is an unprecedented amount of human waste to be treated. In this treatment, pathogenic microbes (bacteria, viruses, protozoa, and parasitic worms) must be removed or reduced to harmless levels. It is well known that in any community, at any time, there are always small numbers of people who are either manifestly ill, in some stage of illness but not demonstratively so, or healthy carriers of diseases. Together, these are indications of a communityís normal background of pathogenic microorganisms in which feces are in the sewage. As a result, sewage is a great threat to human health, especially for those who come in contact with water drawn from sewage contaminated sources.

Generally, sewage consists of 99.9% water and 0.02% solids. Although the amount of solids may seem small, in comparison to the amount of water that is flowed in a large city such as Washington D.C, solids amount to 200 tons/day (Benarde). Of this 40-50% is protein, 40-50% consist of carbohydrates, and the remaining 5-10% is fat (Benarde). All these substances are broken down from fecal matter. Fecal matter is known to be the leading cause of death, with a toll of 10 million a year. Some examples of diseases are typhoid and cholera; these are very common in third world countries, due to the lack of sanitation. In modern industrialized countries, sanitation is taken to higher step than in developing countries. For example in the United States, drinking water runs through a series of treatment steps before it is flowed into households, as for third world countries, water is usually pumped by a well with no treatment at all. Because of this, serious diseases develop in untreated, unsanitary water.

In the United States, several steps are done before water can reach a household. The first process to treat water is the primary treatment, sewage goes to a treatment plant, in the treatment plant the untreated water flows through coarse and fine screens to trap floating objects such as fecal solids and other items. The coarse screens consist of a bank of vertical bars set approximately 1 inch apart. Behind the screens is a comminutor, which grinds the remaining solids to a size that should prevent damage to the machinery that later are used to filter (Benarde).

The following step is secondary treatment, depending on the type of secondary treatment to be given; the sewage will pass to either a bio-filter or an activated sludge aeration tank. Both are based on the stabilization or neutralization or organic waste by biological action. Although pathogenic microorganisms are partially removed in the settling process and filtration and aeration mechanically remove others, it is the process of chlorination that destroys the great majority of organisms. In addition, chlorine leaves a residual in the water system can further disinfect, as water is discharged into the watercourse.

Water supplies were first chlorinated at the turn of the century, and over the following two decades chlorination was introduced for the disinfecting of drinking water in industrialized countries. In the chlorination process, chlorine reacts mainly with natural water constituents to produce a complex mixture of by-products, including a wide variety of halogenated compounds, the actual levels of which depend on the amount of chlorine added and the type of water source. Estimates of the total halogenated organic matter generated during chlorination suggest levels ranging from 10-250 micrograms/liter of chlorine (Groups, webpage). The main chlorination by-products are trihalomenthanes and chlorinated acetic acids. These by-products are responsible for most of the bacterial mutagenicity found in chlorinated drinking water. The formation of trihalomethanes occurs when organic material is reintroduced to treat water. The chlorine residual left from secondary treatment reacts with the organic material to produce trihalomethanes, highly mutagenic and carcinogenic solvents.

Over the years, there has been several cases researched that have without unreasonable doubt led a strong connection of serious health hazards due to chlorinated water. In the latest study, Drinking Water Mutagenicity and Gastrointestinal and Urinary Tract Cancers: an Ecological Study in Finland, reported in the American Journal of Public Health (August, 1994), a study was done on 56 Finnish municipalities and is the largest long term study ever done. The purpose of this study was to investigate the relationship between exposure to mutagenic drinking water and cancers of the gastrointestinal and urinary tract. Statistically significant exposure-response association was observed between exposure to chlorinated water and incidence of bladder, kidney and stomach cancers. In an ordinary municipality using chlorinated surface water, this exposure would indicate a relative risk of 1.2 for bladder cancer and 1.2 to 1.4 for kidney cancer compared with municipalities where non-mutagenic drinking water was consumed. This is a direct relationship, chlorinated water and cancers. Another example is chlorine has been documented to aggravate asthma, especially in those children who frequently use chlorinated swimming pools. Several studies also link chlorine and chlorinated by-products to a greater incidence of bladder, breast and bowel cancer. If there is such a high health risk, why is chlorine used? It is believed to be the most cost-effective way to treat water thoroughly. Government officials feel that the sacrifice of a few cases of cancer and other health problems is well worth it, in comparison to no sanitary water at all. This is an acceptable notion, but with the technology enhanced in industrialized countries, there are several other alternatives.

One of the best, but more cost effective ways to treat drinking water is through ozone. Ozone is bubbled through the water, breaking down all parasites, bacteria, and all other harmful organic substances. Chloroamines is also another alternative, its good because it does not form trihalomethanes, but it also doesnít leave a residual, which may be bad, because drinking water can contain bacteria and other harmful substances. From the three different choices given to treat drinking water, chlorine seems to be the most effective. In a population of one million people its believed that 56 will get cancer when water is treated with chlorine, 11.8 will get cancer with Chloroamines, and 63 will get cancer with ozone (Stern). This shows of the following three, chlorine would be the best choice, it may be questioned why not Chloroamines, Chloroamines donít due a great job of killing pathogens. Until there is another alternative to safer drinking water, the only educated alternative is to use home filtration apparatus. In general, these filtration units take out over 90% of the chlorine available to a glass of treated water.




Benarde, Melvin A. Our Precarious Habitat (fifteen Years Later). Chapter 11. John Wiley & Sons, New York.

Group 3. Chlorinated Drinking Water. Web page.



McAdam, Thelma. Chloramine in Water Supplies Poses Hazardous to Plants and Fish. Hans home page @

McAdam, Thelma. Finnish Study Links Chlorinated Water to Cancer. Hans home page @

Rona, Zoltan. Rethinking Chlorinated Tap Water. Web page.

Sneed, David. State water pipeline leaks chlorinated water, killing fish. Web page.

Stern, Sherry. Enviromental Quality and Health. Spring Quarter lecture.