Disinfection Method

Columbia Water & Light uses a combination of chlorines and chloramines to disinfect its water supply before distribution.  This method was approved by the Missouri Department of Resources and reduces the formation of trihalomethanes in our water.

Why is chloramine disinfection used?

Until August 2009, Columbia Water & Light used the chlorine disinfection method. The switch to chloramine disinfection was made after the levels of total trihalomethanes (TTHM) exceeded the maximum contaminant level of 80 micrograms per liter in 2008. Research showed that the chloramine disinfection process would slow the formation of TTHM. Both the Missouri Department of Natural Resources and the Columbia City Council approved switching to this disinfection method. After the disinfection method was changed, the amount of TTHM dropped by at least 50%.  

What are chloramines?Treatment

Chloramines are formed when ammonia is added to chlorinated water. Chlorine kills bacteria, viruses and other organisms that could cause serious waterborne illnesses and death. A small amount of ammonia is then added to stop the formation of disinfection by-products. The chloramine disinfection process has been used by water utilities for almost 90 years. Over 68 million people in the United States drink water disinfected with the chloramine method.

How much ammonia is added to Columbia’s water?

Approximately two milligrams per liter. For comparison, this would be similar to adding six grains of table salt to a one gallon container of water.

Is chloraminated water safe to use?

Chloraminated water is safe for drinking, bathing, cooking, gardening and other household tasks. Chloramines must be removed before using the water in fish tanks. Products for chloramine removal are available through aquarium supply stores. As with chlorine, the chloramines should be removed from the water when used in kidney dialysis machines. Patients undergoing dialysis should check with their doctors about the dialysis filtering method being used.

Is the chlorine disinfection method ever used?

Yes. The Missouri Department of Natural Resources recommends Columbia switch to the chlorine disinfection method for a brief period each year. Chlorine helps clean any nitrate build up in the distribution system that could aid bacterial growth. Generally the change of disinfection methods happens in the spring/summer. Customers might notice the water has a stronger chlorine taste during this time.

What are Trihalomethanes?

Trihalomethanes are a by-product of the disinfection process. They are formed when chlorine breaks down organic material in the water. Trihalomethanes may present problems over a long period of time. Long-term exposure to levels that exceed the maximum contaminant level is a health concern. When the amount is exceeded, consuming two liters of water per day for over 70 years could result in three to four cancers per 10,000 people. According to the Environmental Protection Agency, people drinking water exceeding the standards for trihalomethanes over a long period of time might also experience problems with their liver, kidneys or central nervous system, which is why they lowered the maximum contaminant level for total trihalomethanes in 2004. 

What W&L is doing to reduce levels of Trihalomethanes?

The levels of trihalomethanes have fluctuated and seasonally the levels have gone up over the years.  The water distribution system has also grown substantially since the water treatment plant was built and it takes longer Water Testingfor the water to reach the furthest parts of the distribution system. This means there is more time for the chemical reaction between the organic material and the chlorine to form Trihalomethanes. In order to keep the levels of trihalomethanes low, the city switched to the chloramine disinfection method as approved by the Missouri Department of Natural Resources. For more detailed information, please see the 2009 Water Resources Research Center’s final report  on disinfection by-products in Columbia’s water system.