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Disinfection Byproducts

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Disinfection, sometimes referred to loosely as chlorination, is a necessary part of the water treatment process. It kills pathogens, and it produces chemical byproducts. Disinfection is typically done by adding small amounts of a chlorine-based disinfectant to water. It destroys water-borne microbes, bacteria, and viruses — organisms that can cause serious illnesses or death. Typhoid and cholera, which have killed hundreds of thousands of people in global epidemics, have been controlled in the United States through the addition of disinfectant to drinking water.

Denver Water has to be diligent to keep bacteria out of our water. There is a possibility that microorganisms might get into treated water after it leaves the treatment plant. This is why public health regulations require that tiny but detectable amounts of disinfectant must remain in the water all the way to the tap. Disinfectant ensures that the water coming from your tap is free of pathogens.

So small amounts of disinfectant are added to the water before it leaves the plant. And as the disinfectant reacts with organic substances in the water, byproducts are created.

The Environmental Protection Agency regulates the quality of drinking water on a federal level. Its regulations cover acceptable, safe levels of microorganisms, disinfectant, and disinfection byproducts. In December 2005, after a lengthy review process which included water providers and environmental groups, the EPA added two new rules to the Safe Drinking Water Act: one modifies the old rules for measuring the byproducts of disinfecting potable water (DBP2) and the other regulates protection against disease-causing microorganisms (LT2).

The LT2 regulation deals primarily with Cryptosporidium. Denver Water has been monitoring for "Crypto" for decades, and testing has never detected any in treated water (and very little if any in the raw water). The situation regarding disinfection byproducts (DBPs) is not so simple, though.


The term "disinfection byproducts" covers a host of compounds that may be formed after water is treated. Depending on the substances present in the water, a wide range of byproducts may be created. But the only reliable approach to protecting against bacteria in drinking water is to add a disinfectant, which must travel with the water, in minute amounts, all the way to your tap. And any disinfectant creates disinfection byproducts. There is little evidence that these chemicals are dangerous at the level they occur in treated water, but research on the potential effects of specific compounds raised concerns with the EPA.

Like many problems, there is no easy answer. As the EPA report says, "Decreasing disinfection byproduct risk could increase risks from disease-causing microorganisms." The paradox is as old as the use of fire to keep warm: It keeps you from freezing, but it also produces ash and carbon monoxide. Denver Water has spent millions of dollars to upgrade our treatment plants to specifically reduce the concentration of disinfection byproducts in the drinking water.

The trick with disinfectants is to balance the beneficial effects against the unknown ones.
Because Denver’s water is collected high upstream, above major agricultural or municipal developments, organic materials are much less of a problem than they are for treatment facilities farther away from the origin point of the water. Organic content is a naturally occurring part of fresh ("raw") water, and it must be controlled. Our process ensures that the water is safe to drink. Testing to verify the quality of that raw water and the effectiveness of the treatment are important parts of the water quality process. Because the concentration of organic material is low, the amount of disinfection byproducts created is also low.

How dangerous are disinfection byproducts?

Some medical research suggests that specific DBPs (total trihalomethanes and haloacetic acids, referred to as TTHMs and HAA5 may cause a variety of medical conditions, including some forms of cancer and miscarriage. Thirty years of research have not provided definitive results, only sparse and inconsistent findings. But even the possibility of very minor effects is a concern to water systems and the public, which is why the EPA has established maximum contaminant levels (MCLs) for the suspect DBPs.

To see details on the EPA's research that resulted in the new regulations, go to their SafeWater site.

As shown in our annual water quality reports, Denver Water has been in compliance with the standards, based on testing methods then in place, for some years.

Keeping your water safe is a key part of Denver Water's mission, just as it is the EPA's and that of the Colorado Department of Public Health and Environment. Together, we will see that you do not need to worry about your drinking water.