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Home >> Knowledge Base: How? Why? What? >> Chlorine in Tap Water

Chlorine in Tap Water

Jawad Corbaci,
Chlorine in Tap WaterThe link between water quality and health has been known since the early ages, and boiling drinking water (thermal disinfection) was applied for centuries. In the early nineteenth century -when the effect of chlorine, a chemical disinfectant, was discovered- its use became a common practice by water companies to prevent the distribution of waterborne diseases. At the time, water contaminated with pathogens was a leading cause of death worldwide. Chlorine in the form of Sodium hypochlorite solution (NaOCl) is a commonly used household cleaner (i.e., bleach) and it is also used as a disinfectant in municipal water supplies at low concentrations (e.g., 1 ppm). Municipalities are required by the Environmental Protection Agency (EPA) to ensure that water delivered to customers (you and me) is at least 95% clear of coliform bacteria. For many municipalities, adding chlorine to kill bacteria is the easiest way to comply with this regulatory requirement.

The use of filtration for turbid water is centuries old, as people always considered clear water to be clean water. Swamp areas were always associated with illness. For the past centuries, humans suffered from waterborne diseases such as cholera (spread by the bacterium Vibrio cholerae) and Giardiasis (caused by Giardia lamblia Protozoan). The use of chlorination minimized the cholera epidemic in many parts of the world.

Since the presence of pathogens such as giardia and fecal coliform bacteria is more common in surface water, water companies and municipalities serving communities on water supply from rivers and lakes provide both filtration and chlorination in central treatment plants before delivery to customers, as required by local and federal regulations.

The City of Chicago utilizes Lake Michigan water—a surface water source-- via two water treatment plants, and they publish an annual water quality report to keep customers informed, as required by federal regulations. In its 2012 Water Quality Report, the City of Chicago reported that Giardia was detected in raw water in September 2010. The use of both filtration and hypochlorination (using sodium hypochlorite or liquid chlorine) can be understood in this case, and in all areas that depend on surface water. The same 2012 report documents the presence of disinfection byproducts (e.g., trihalomethanes) at one forth of the allowed limit. So, the City is within regulations. Chlorine is in our tap water, as required by the same surface water treatment regulations. So, we drink chlorinated water; is it safe?

The function of filtration in treatment plants is to reduce turbidity and remove microorganisms. Chlorination inactivates any microorganisms that make it through filtration and the contamination-removal process. Undeniably, chlorination has improved the quality of life for humans worldwide. Yet chlorination has its problems, and can be viewed as a “minimal” treatment--much like a physician avoiding hyper--drugging a patient. There’s the prevalent scientific theory that chlorine and its byproducts are carcinogens. When it mixes with the organic material in surface water, trihalomethanes are formed, a compound long associated with cancer and birth defects. DeVito and other toxicologists hint that the same sodium hypochlorite may also be killing (or inactivating) useful bacteria in our intestines. So, perhaps chlorinated water may not be so safe, despite its immense disinfection benefits.

So, chlorine has disinfection functions before reaching the tap, but there remains the issue of removing it before ingestion. Chlorine prevents the growth of bacteria and other microorganisms while traveling miles of pipes to your kitchen sink, but it’s theorized that removing it before human consumption—especially drinking—makes water safe.

Chlorine can be removed effectively using any carbon filter. That explains the wide spread of carbon filters for chlorinated tap water. Is chlorinated water safe? The presence of chlorine in water may be the easiest way to ensure delivering water that is bacteriologically safe. Chlorine will do the same thing when entering our bodies, killing useful organisms in our intestines. It may also cause the formation of disinfection byproducts, with all its adverse health effects. Customers should know that the responsibility of water companies stop at the water meter.

The use of chlorination was extended and promoted to many public water systems using groundwater, even when it is not needed. Like using the chemical calcium propionate (preservative) in bread to extend the shelf life of the bread, companies may use chlorine to mask any bacteriological problem at the well. If your baked bread is kept in a refrigerator or freezer or used within two days, is there a need for a preservative? Using the same trail of thought, if water facilities in groundwater systems (wells, storage tanks and pipes) are kept clean and fresh, is there a need to provide chlorination?

In the same 2012 report, the City of Chicago stated that surface water intakes are located at a distance offshore to minimize the impact of shoreline activities on water quality. However, the same report mentioned that the intake crib structures attract waterfowls, thereby concentrating fecal deposits at the intake. Instead of pumping offshore, the City of Chicago can pump water from deep wells, located inland at a distance, say 200 ft from the shore. Pumping from aquifers that are hydraulically connected to Lake Michigan will provide natural filtration before water enters the surface water treatment plants.

The widespread use of bottled water and carbon-based water filtration systems, including reverse osmosis systems, is the natural response by the industry to meet the needs and challenges that public agencies and public water system stop short to address. Many people find chlorine taste and odor objectionable. In addition, high levels of chlorine irritate the eyes, skin, etc.

Most economy filtration system and Reverse Osmosis Water systems have carbon filters, and therefore remove chlorine before water goes through the RO membrane, as chlorine will damage the membrane.