You probably already know that most public utilities use chlorine in tap water as a disinfectant. But how to know exactly how much is in your drinking water and if are you at risk from consuming it?
This article will break down everything you need to know about chlorination in your water supply. I will show how to detect if you have an unsafe amount of chlorine, and most importantly, how to treat it if you do.
- Chlorine is a disinfectant added to public drinking water systems to kill harmful microorganisms in the water supply.
- The EPA has a Maximum Residual Disinfectant Level for chlorine of 4 mg/L.
- Extended exposure to trihalomethanes and other disinfection by-products can increase the risk of cancer.
- The most accurate way to detect chlorine concentration levels in your water is with a certified lab test.
- The best treatment method to remove chlorine from water include catalytic carbon and reverse osmosis filtration.
Why Is There Chlorine In Tap Water?
Chlorine was first used as a drinking water disinfectant in the late 1800s to reduce the prevalence of waterborne diseases, such as cholera and typhoid fever. Chlorination continues to be used in drinking water systems across the United States to kill germs like norovirus, salmonella, and campylobacter. In fact, nearly 70% of public water systems are using chlorine treatment to disinfect water.
Since our water comes from various sources like lakes and wells, adding chlorine to water removes harmful bacteria to aid in water disinfection, otherwise known as chlorination. Water can also pick up contaminants as it travels through miles of plumbing before reaching your tap, which is also addressed by water chlorination.
Keeping the general public water supply clear of harmful bacteria is extremely important for public health, and chlorine is responsible for ensuring your tap water is safe to drink. Although alternative methods of disinfection are now available, chlorine has stood the test of time. Chlorination is still the most cost-effective way to remove the risk of waterborne disease outbreaks.
How Much Chlorine Is In Tap Water?
The chlorine level required to treat all impurities in water is called “chlorine demand.” Once this level has been met, breakpoint chlorination has occurred. That is the amount of chlorine needed before free chlorine can be produced.
After reaching the breakpoint, additional chlorine added to the water supply will result in a free chlorine residual. Residual chlorine is the difference between the amount of chlorine added and the chlorine demand. Most water treatment plants will add chlorine beyond the breakpoint to ensure the water supplies are properly disinfected.
You can check if there is a disinfectant in your water, what type of disinfectant is being used, and whether your utility has followed drinking water chlorination rules by looking at the utility’s consumer confidence reports (CCR).
According to the WHO, most people can taste or smell chlorine in water at lower concentrations than 4-5 milligrams. This estimated threshold means that if there were dangerous amounts of chlorine in your tap water, your senses would likely pick up on it.
How Does Chlorine Kill Microorganisms?
Chlorine damages the microorganism’s cell membrane in order to deactivate it. When the cell membrane is weakened, chlorine enters the cell and disrupts the DNA activity and cell respiration, whereby the cell eventually dies.
The overall effectiveness of disinfection depends on the chlorine concentration and contact time with the water. The higher the concentration and contact time, the more effective it is. However, there is a negative relationship between contact time and concentration, meaning the higher the concentration, the lower the required contact time, and vice versa.
For this reason, chlorine is typically used by public water systems as the primary disinfectant and chloramines as the secondary disinfectant to adhere to disinfection byproduct regulations.
Types Of Chlorine Used For Water Disinfection
Adding any form of chlorine to water during the treatment process will form the main disinfecting compounds in chlorinated water, which are hypochlorite ions (OCl-) and hypochlorous acid (HOCl).
For Example: Chlorine Agent + H2O = OCl- + HOCl
However, disinfection does not have to be carried out with pure chlorine, but also with chlorine-containing substances. The most common types of chlorine used in water treatment are sodium hypochlorite, calcium hypochlorite, and chlorine gas.
- Sodium hypochlorite: Sodium hypochlorite (NaOCl) is made of sodium salts from hypochlorous acid. It is a transparent light yellow liquid that is very corrosive. Sodium hypochlorite is the easiest to handle out of the different types of chlorine available.
- Calcium hypochlorite: Calcium hypochlorite (CaOCl) is made of calcium salts from hypochlorous acid. Calcium hypochlorite is a solid white material that comes in either granular powder or tablets.
- Chlorine gas: Chlorine gas comes in a compressed liquid form that has a greenish-yellowish color. Chlorine gas is the most cost-effective form of chlorine used to treat water. When added to water it will create hypochlorous acid (HOCl) which then dissociates into hydrogen ions (H+) and hypochlorite ions (OCl-).
What Are Safe Chlorine Levels In Drinking Water
If within acceptable levels, chlorinated water is safe to drink. According to the U.S. Environmental Protection Agency (EPA), the amount of chlorine that is safe to be consumed is no more than 4 milligrams per liter. The agency states that levels below this are unlikely to cause harmful effects or increase long-term health risks.
The World Health Organization (WHO) also has set guidelines for chlorine in drinking water quality (GDWQ) at 5 milligrams per liter.
Water quality levels must be adhered to by water treatment plants or they will face punishment from the relevant authorities. If you smell or taste chlorine in your water, it might be worth getting a test to check if it is within an acceptable range.
However, the byproducts of chlorination come with greater public health concerns. A certified lab test should not only test for chlorine but also for disinfection byproducts (DBPs).
Side Effects Of Too Much Chlorine In Drinking Water
Chlorine exposure in drinking water is typically very low and not an overall danger. However, at high levels, it can be toxic not only for bacteria but for humans as well. Some common side effects of elevated chlorine in water are:
- Stomach aches
- Itchy skin
- Dry skin
These side effects are usually associated with ingesting chlorine in larger quantities than you would normally find in your drinking water, as these levels are strictly regulated. The greater concern is from extended exposure to trihalomethanes and other disinfection by-products, which are chlorination by-products of chlorination. Increased exposure to these carcinogens can lead to increased risk of bladder, rectal, and colon cancer.
Additionally, accidentally drinking water from swimming pools, where chlorine levels are much higher and water quality is lower, may result in some of the symptoms above. Or consuming well water before properly flushing the system following a shock treatment.
A concern about elevated chlorine in drinking water is the potential effect on the gut microbiome, especially in children and vulnerable populations. The theory is that while yes, chlorine kills the bad bacteria in water, it can also kill some of the good bacteria in our guts. Some research in mice supports this theory.
However, this 2022 study in Bangladesh suggests that chlorinated tap water did not negatively affect the gut microbiome in young children. Again, the EPA has no listed health effects from drinking chlorinated tap water, but more research is needed on the matter.
How To Test For Chlorinated Tap Water
If you find yourself wondering if your drinking water is dangerous, then you can investigate using a home test strip or a certified lab test. Testing your water will indicate if there is too much chlorine in your tap water and if the concentration is higher than the regulatory limit.
Certified Lab Test
The most accurate way to measure chlorine is to use a certified lab test with your tap water. The good thing with a lab test is it will analyze not only chlorine but also a range of DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs).
I recommend using the Freshnss Labs water test kit which analyzes dozens of harmful contaminants in a certified lab. Simply collect a water sample in the provided vial and send it back to the lab. You will then receive a detailed report with all detected contaminants, any health or plumbing alerts, and the best treatment methods based on your data.
Laboratory Water Test Kit
Analyzed in a certified laboratory
Includes detailed report with EPA benchmarking and safety concerns
As mentioned above, the most concerning issue around chlorine treatment is the byproducts it produces. The CDC states that chronic exposure to DBPs may increase cancer risk. When chlorine interacts with organic matter in water, it produces byproducts, the major ones being:
- Trihalomethanes (THM)
- Haloacetic acids (HAA)
The EPA developed stage one and stage two disinfectant byproduct rules (DBPRs) to address this matter. However, the agency strongly recommends that individuals increase their awareness regarding their drinking water. This may be done through consumer confidence reports (CCRs), contacting their local water treatment plant, and proper lab testing.
Chlorine Test Strips
Chlorine test strips are a simple and quick way to check the levels of chlorine in your drinking water. You simply dip the strip into a glass of tap water and match the resulting color of the strip with the packaging, to ascertain how much chlorine is present. These tests are available for approximately $20 online or at a variety of local retail stores.
The downside of using DIY test strips is they are less accurate than using a laboratory test, and they do not provide the precise level of chlorine detected. However, they are an ideal solution for spot-checking chlorination levels.
How To Remove Chlorine In Drinking Water
If you find elevated levels of chlorine in your water, you can either contact your water system or invest in a water filtration system, or both. Here are the best water filtration system options to reduce exposure to chlorine in drinking water at home.
Granular Activated Carbon Filter
A granular activated carbon filter, or GAC filter for short, can be an effective water treatment to remove excess chlorine. A GAC filter uses materials high in carbon, such as coconut shells, to remove chlorine and other organic chemicals. The water passes through a high-density carbon filter and the chemicals are attracted and absorbed by the carbon within.
A GAC filter does have a limited shelf life and should be changed regularly. The frequency of changing your filter is determined by the levels of chlorine and other substances in your area’s water supply. A GAC filter will not filter out other compounds such as iron or nitrate.
Catalytic Activated Carbon Filters
A catalytic activated carbon filter works similarly to a GAC but with one key difference. The carbon in a catalytic-activated filter undergoes a technical process that changes the ionic structure of the carbon. This process gives the carbon a greater ability to reduce chlorine and other compounds with the need for far less contact time.
These filters also have the ability to retain oxygen, helping to further reduce by-products of carbon filtration like ammonia from the water. A catalytic carbon filter is likely to cost more than a GAC due to the higher standard of filtration.
Reverse osmosis filters out contaminants such as chlorine as well as disinfection byproducts, making your water safe to drink. The reverse osmosis process works by passing water through a semi-permeable membrane which allows water molecules small enough to get through, however harmful chemicals and compounds are too large to pass through.
Frequently Asked Questions
Is chlorinated water bad for you?
In small doses, the U.S. Environmental Protection Agency (EPA) suggests that chlorine in drinking water is safe for human consumption. Additionally, there has been no indication from the EPA that there are long-term health risks associated with drinking the regulated amount of chlorine in water.
Does bottled water have chlorine in it?
The FDA categorizes bottled water by its origins. The four categories are artesian well water, mineral water, spring water, and well water. Each of these origins will have a varying level of chlorine upon extraction. In some cases, bottled water will have chlorine in it. In other cases, the water may have gone through a reverse osmosis filtration system and have none.
Does boiling water remove chlorine?
Boiling water is an effective way to remove chlorine in drinking water. The process of boiling the water drives dissolved gases such as chlorine into the air and out of your water. However, this will not remove chloramine unless the water is boiled for over 20 minutes. Another thing to note is that this process is best performed when the water covers a large surface area, so using a larger pan is more effective.
Can water softener systems remove chlorine?
Water softeners do not remove chlorine from your drinking water, so a water softener should not be considered as a filtration system. However, water softeners are specifically useful for softening water by removing hard water minerals such as calcium and magnesium.