Water Quality Treatment

The Disinfection Process

The water disinfectant switch from chloramine to chlorine once a year is a step in the water treatment process to assure the biological safety of our drinking water.

Disinfection is a step in the water treatment process to assure the biological safety of water. Chlorine, chloramines and other chemicals can be used as disinfectants. In 2000, the Washington Aqueduct, which provides drinking water for Arlington residents, switched to chloramine as its disinfectant.



Chloramine is formed when ammonia is added to water that contains free chlorine. Depending on the pH and amount of ammonia, the ammonia reacts to form one of three chloramine compounds. NH2Cl, or monochloramine, is the preferred compound and the one produced by the Washington Aqueduct.

Why did our water provider change from chlorine to chloramine disinfectant in 2000?

A regulation by the Environmental Protection Agency (EPA), the Stage 1 Disinfectant and Disinfection Byproduct Rule, requires water producers to limit chemical compounds known as disinfection byproducts, which include trihalomethanes (THMs). There’s some concern that THMs may be potential carcinogens. The addition of chloramine to the disinfection process quenches the production of chlorine byproducts (THMs). As when using chlorine as a disinfectant, water treated with chloramine leaves the treatment plant with most bacteria killed or inactivated, but unlike chlorine, the reaction that produces THMs is arrested and the level of those chemicals in the water delivered to customers is substantially reduced. Additionally, there’s now less of a chlorine taste and odor in the water.

Is chloramine safe?

Chloramine is safe. The EPA accepts chloramine as a disinfectant and recognizes its ability to control THM formation. Chloraminated water is safe for bathing, drinking, cooking and everyday uses.

Why does our water provider change back to chlorine as the disinfectant every spring while the water mains are flushed?

Every year for approximately six weeks, we switch disinfectants from chloramine back to chlorine to flush out the water distribution system and improve water quality. A biological film, known as biofilm, is found in all water pipes and can lead to water quality problems if not controlled. Biofilm can become accustomed to the chloramine disinfectant that is routinely used. By switching to free chlorine for a short period of time, the biofilm is “shocked” and weakened. Using fire hydrants to conduct a systemwide flushing of our distribution mains, combined with the disinfectant change, is a very effective method for controlling biofilm; this process is used nationwide.

What methods are available to remove chloramine?

Carbon filtration or water treatment products that neutralize chloramine may be used. If you use a carbon filter it must contain high-quality granular-activated carbon and you must permit sufficient contact time.

Will reverse osmosis remove chloramine?

No. Salts can be caught by the permeable membranes, but chloramine may pass through the membranes.

Do home water softeners remove chloramine?

Most softeners are not designed to remove chloramine.

At Home

What about fish tank owners?

Fish tank owners, including hobbyists, restaurants and fish markets, who now treat for chlorines in the water, should verify that they have appropriate carbon filtration equipment or use water treatment products that neutralize chloramine. These products are readily available through pet and aquarium stores, as well as from companies that service commercial fish tanks.

Does letting water sit for a few days remove chloramine from fish tanks?

No. Unlike chlorine, which breaks up when water sits for a few days, chloramine may take weeks to disappear. If you choose not to use de-chloraminating chemicals, install a granular-activated carbon filter and allow sufficient contact time between the water and filter.

Will chloramine affect the way I treat my swimming pool?

No. You’ll still need a chlorine residual to retard algae and bacteria growths.

Your Health

Can children and pregnant women drink chloraminated water?

Yes, everyone can drink water containing chloramine.

Can people on low-sodium diets or those with diabetes use chloraminated water?

Yes. They can use chloraminated water for all purposes.

How about washing an open wound with chloraminated water?

Even large amounts of chloraminated water used in cleaning a cut would have no effect because virtually no water enters the bloodstream this way.

Kidney Dialysis Patients

What does this mean for kidney dialysis patients?

Drinking either chlorinated or chloraminated water is safe. Chlorine and chloramines are harmful only when they directly enter the bloodstream through the dialysis process. As a result, you may need to change the way water is pretreated for dialysis. Depending on the method of chlorine removal your dialysis machine uses now, some modifications may be necessary.

Why do kidney dialysis patients need to take special precautions?

In the dialysis process, the compounds in water come in contact with blood across a permeable membrane. Chloramines in that water would be harmful, just as chlorine is harmful, and must be removed from water used in kidney dialysis machines. There are two ways to do that: either by adding ascorbic acid or by using a granular-activated carbon treatment. Medical centers that perform dialysis are responsible for preparing the water that enters dialysis machines. They’ve been informed of this change.

Is it safe for kidney dialysis patients to drink water containing chloramines?

Yes. Because the digestive process metabolizes chloramines before they reach the bloodstream, everyone can drink chloraminated water. Kidney dialysis patients can drink, cook with and bathe in chloraminated water. It’s only a concern when water interacts directly with the bloodstream, as in dialysis.

What should people with home dialysis machines do to remove chloramines?

You should first check with your dialysis physician, who will probably recommend the proper type of water treatment. Often, home dialysis service companies can make the needed modifications, but you should check with your physician to be certain.

Do medical centers, hospitals and clinics that perform kidney dialysis know about the change to chloramines?

Yes. All medical facilities have been notified of the change. All dialysis systems prepare the water being used for dialysis. If you have any concerns about this process, talk with your physician.