Drinking Water Chlorination: Frequently Asked Questions

What is drinking water chlorination?

Drinking water chlorination is the addition of chlorine to drinking water systems. It is the most common type of drinking water disinfection. Disinfection kills bacteria, viruses, and other microorganisms that cause disease and immediate illness. Chlorine is effective and continues to keep the water safe as it travels from the treatment plant to the consumer's tap.

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A little over 100 years ago, waterborne diseases like typhoid fever and dysentery were a common part of life in the United States —and a common cause of death, too. In the early s, cities started disinfecting drinking water supplies to kill bacteria, viruses, and other microorganisms. Both the World Health Organization and the Centers for Disease Control and Prevention regard disinfection of drinking water as one of the most important advances in public health.

To learn more about drinking water disinfection, visit Disinfection and Disinfection Byproducts.

Is drinking water chlorination required?

Chlorination or other continuous disinfection (disinfection that protects from the treatment plant to the consumer’s tap) is required for public water systems that:

• Use surface water, such as rivers, lakes, and streams, as their source;
• Have treatment processes that expose the water to outside or open air; or
• Add treatment chemicals for corrosion control; these chemicals can feed microorganisms and cause them to grow.
• Disinfection is recommended but not required for other community public water systems.

Is chlorinated water safe to drink?

Yes. The U.S. Environmental Protection Agency (EPA) limits the amount of chlorine in drinking water to levels that are safe for human consumption. The levels of chlorine used for drinking water disinfection are unlikely to cause long-term health effects.

During water treatment, chlorine can combine with naturally occurring organic matter in the water to form compounds called disinfection byproducts (DBPs). DBPs can cause negative health effects after regular, long-term exposure.

The EPA has set limits for several types of DBPs. All public water systems that disinfect must regularly test their treated water to measure levels of regulated DBPs. If they are above the limits set by EPA, the water system must take action to reduce the DBPs. This action includes notifying all of their customers of the DBP levels.

The Minnesota Department of Health sets health-based guidance values for some DBPs. These values are protective for the most sensitive and/or highly exposed populations. Minnesota’s public water systems are not required to meet health-based guidance values; they may use guidance values as goals, benchmarks, or indicators of potential concern.  Learn more at Guidance Values and Standards for Contaminants in Drinking Water.

What can water systems do about taste and/or smell from chlorination?

When a system first starts chlorinating, it is normal for people to say they can taste and/or smell the chlorine. Over time, the system stabilizes, and any tastes or smells will decrease or go away. People also usually get used to chlorine in water over time.

Public water systems work hard to keep the level of chlorine in the water at a level that effectively disinfects, while keeping taste and odor to a minimum.

Is there anything I can do about the taste and/or smell?

If you are bothered by the taste or smell, there are a few things you can do:

• Put a pitcher of water in the refrigerator and let it sit uncovered for a few hours. This will allow the chlorine smell to leave the water.
• Use cold water for all drinking water. Cold water has fewer taste and smell concerns. (Using cold water also makes the water less likely to absorb lead and copper from plumbing.)
• Use a filter. All water treatment units, even those in your home, require regular maintenance to work properly. Water treatment units that are not properly maintained will lose their effectiveness over time. In some cases, unmaintained units can make water quality worse and make you sick.
  • Most common point-of-use filters (e.g. pitcher filters) will remove chlorine taste and smell.
  • Granular activated carbon filters will remove chlorine taste and smell. They can be more effective, but are usually more expensive than point-of-use filters. They can be installed either at the tap/sink or as whole-house filters.
  • Learn more at Home Water Treatment.

Are there other options for disinfection besides chlorination?

Besides chlorine, there are several other types of disinfectants. Each has tradeoffs. Chloramines may form lower levels of regulated DBPs than chlorine, but, depending on the source water characteristics, they have the potential to form other DBPs and increase the risks of nitrate formation and corrosion in the distribution system. Ozone is effective and has no taste, but it can also create other DBPs and does not provide protection in the distribution system, so chloramines or chlorine must still be added to protect the water. Ultraviolet (UV) light is effective in clear water and does not form DBPs. But like ozone, UV light does not provide protection in the distribution system, so chloramines or chlorine must still be added to protect water from the treatment plant to the tap.

What about bathing or showering with chlorinated water?

Chlorine does not get into the body through your skin. The amount of chlorine in the water is too low to cause breathing problems. Some people who are very sensitive to chlorine could experience skin irritation. Because the amount of chlorine in drinking water is extremely small – far less than in a swimming pool – this situation is expected to be rare.

Disinfection byproducts (DBP) can be inhaled or absorbed through the skin during activities like bathing and showering. There is limited information about the health risks of breathing or coming in to contact with DBPs. Point-of-use filtration devices can be used to lower DBP levels in water.

Does chlorine affect home water treatment, like water softening?

Chlorination will not affect the operation of common home water treatment units, such as water softeners and pitchers. You should always follow the manufacturer’s recommendations for installation, cleaning, and maintenance of a water treatment unit.

Every year waterborne disease outbreaks occur because of public water distribution system deficiencies. A significant number of these outbreaks are caused by broken water mains or contamination of water mains during construction or repair. Disease outbreaks emphasize the importance of using proper procedures and methods when repairing water mains.

To prevent waterborne disease outbreaks, every supplier of water for a public water system must disinfect all newly constructed or repaired water distribution mains by the methods and procedures proposed by the American Water Works Association (AWWA) standards. Calcium hypochlorite granules shall disinfect new water mains before they are placed in service.

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Disinfection of New Water Mains by Calcium Hypochlorite Granules

The use of calcium hypochlorite for disinfection is a relatively simple and cost-effective process that does not require extensive technical expertise. It can handle supply systems of varying sizes by altering dosing systems or storage for chemical contact. The calcium hypochlorite granules are a powerful disinfectant; it kills almost 99.9 percent of all germs (bacteria, viruses, and mildew) and makes the water flowing through potable water lines clean and healthy.

How is Calcium Hypochlorite Applied to New Water Mains?

AWWA C651-14 standard can be used as a guide for the preparation of water mains, application of calcium hypochlorite, sampling, and testing for the presence of coliform bacteria. Calcium hypochlorite conforming to AWWA B300 is available in granular form and must contain approximately 65 percent available chlorine by weight. The material should be stored in a cool, dry, and dark environment to curtail its deterioration. Disinfection of water mains should be done by contractors that install underground water pipelines with calcium hypochlorite as per AWWA standards. Water testing would then be performed in the water utility lab or by a third-party testing provider.

For new mains, sets of samples shall be collected after every 1,200 feet (370 m) of the new water main, and one set from the end of the pipeline and at least one from each branch longer than one pipe length. Disease outbreaks emphasize the importance of using proper procedures and methods when disinfecting water mains using calcium hypochlorite granules to ensure safe and clean water passage through potable water lines.

Methods of Disinfection by Calcium Hypochlorite

The Tablet Method is generally used for disinfection of water mains of 12 inch and smaller diameter mains. The tablet method consists of placing calcium hypochlorite granules or tablets in the water main during installation and then filling the main with potable water to create a calcium hypochlorite solution.

This method may be used only if the pipes and appurtenances are kept clean and dry during installation. The required number of tablets are placed on the inside top of each joint and held in place by approved mastic. The main is then filled with water at a velocity of less than 1 foot per second, and the water is left in the main for at least 24 hours before flushing.

Placement of Calcium Hypochlorite Tablets During Construction

Calcium hypochlorite tablets (5-grams) shall be placed in the upstream end of each section of the pipe to be disinfected, including branch lines. Also, at least one tablet shall be placed in each hydrant outlet and other appurtenances. The chlorinated water shall remain in the pipeline for at least 24 hours. If the water temperature is less than 41°F (5°C), the water shall stay in the pipe for at least 48 hours. The table below shows the number of tablets required for commonly used sizes of pipe.

Number of 5-g calcium hypochlorite tablets for a dose of 25 mg/L

The Slug Method of Chlorination is used for large diameter water mains. It comprises moving a column of highly concentrated calcium hypochlorite water solution (at least 300 mg./L) along with the interior of the pipe with a contact time of a minimum of three hours with the pipe wall. The flushed water should be visually clear and have typical system chlorine residual.

For very-large-diameter pipe (where personnel may safely enter the pipe), instead of flushing following disinfection, the pipe's interior at the repair site may be cleaned by a sweeping and high-pressure wash using potable water before disinfection. Standing water and debris from the cleaning must be removed from the pipe before disinfection. The affected pipe shall be disinfected by swabbing or spraying with a minimum of 1 percent chlorine solution.

After following the appropriate methods above, prior to returning the pipe to service, the disinfection procedure's efficiency shall be verified by testing for the absence of coliform bacteria. If allowed by local regulations, the pipeline may be reverted to limited service before obtaining bacteriological results with proper notification of the affected customers.

Final Flushing

Final flushing can be accomplished, and chlorine residuals checked to determine that the heavily chlorinated water has been removed from the pipeline. After final flushing, bacteriological tests are performed in accordance with state and local regulations to ensure that no coliform organisms are present. 

After the applicable retention period, heavily chlorinated water should not remain in constant contact with the pipe to prevent damage to the pipe lining. To prevent corrosion damage to the pipe itself, the heavily chlorinated water shall be flushed from the main fittings, valves, and branches until chlorine measurements show that the concentration in the water leaving the main is no higher than that generally prevailing in the distribution system or that is acceptable for domestic use.

PLEASE NOTE: When flushing out the chlorinated water, caution should be taken to provide environmentally acceptable disposal.  

ANSI/AWWA 651, the updated Disinfection of Water Mains standard, seeks to clarify steps to take depending on the nature of the work. Given the wide range of projects and repairs, these updates accommodate the variety of conditions that come across and provide a means to assess the risk and identify the appropriate level of disinfection and sampling before any outbreak. Strict compliance with the guideline provided by AWWA standards results in the complete disinfection of the water main and availability of clean water for domestic purposes.

For more on safe drinking water see the list of Iron Strong Blogs below:

• Safe Drinking Water – How Do We Ensure the Highest Standards? by Jerry Regula
• Do You Have an Iron Deficiency? – Considering Health Effects of Pipe Material Selection by Roy Mundy
• How to Protect Water Quality from Permeation Due to Contaminated Soils by John Johnson
• Got Certification? Fabricated Ductile Iron Pipe and NSF/ANSI 61 by Dan Henrie

Need Assistance with Your Waterworks Project?

If you have any questions regarding this topic or anything Ductile iron pipe-related, be sure to reach out to your local McWane Ductile representative. We have team members who've managed small and large water utility systems, served in engineering consulting firms, and bring decades of experience in solving field issues involving pipeline construction and operation. From design to submittal, to installation, we strive to provide education and assistance to water professionals throughout the water and wastewater industry.

Bob Hartzel is the Senior Sales Representative for McWane Ductile, covering the eastern Pennsylvania sales territory.
Bob began his career with the McWane Company in . He started as a Sales Representative covering eastern Pennsylvania. He was later promoted to District Manager of the Mid-Atlantic Territory in . As D.M., he managed sales in PA, NJ, DE, MD, and D.C., while still covering eastern Pennsylvania. In early , his role changed to Senior Sales Representative, responsible for sales in eastern Pennsylvania only.
“I enjoy the relationships I have developed with my customers over the years. Those relationships have become friendships. I enjoy assisting them with troubleshooting issues as well as providing insights to help them meet their goals while providing outstanding customer service,” says Hartzel.
Bob is a graduate of Slippery Rock University with a B.S. in Physical Education with an emphasis in Sport Management. Bob has been a member of the local AWWA, WWOAP Associations, and various contractor associations over the years.
In his spare time, Bob enjoys weight training and exercise, as well as hunting and fishing. He also volunteers at a local food bank handing out Thanksgiving meals.
Bob’s favorite quote: “The only way to do great work is to love what you do.” – Steve Jobs

Contact us to discuss your requirements of water treatment calcium hypochlorite. Our experienced sales team can help you identify the options that best suit your needs.