Chlorine is a widely used chemical disinfectant in municipal water supplies. Its role in public health is undeniable, ensuring drinking water safety by eliminating harmful microorganisms. However, chlorine in water also presents various effects on human health, aesthetics, and the environment.
Chlorine’s Role in Water Treatment
Chlorine is purposefully added to water systems as a potent disinfectant. Its primary function is to destroy or inactivate disease-causing pathogens, including bacteria, viruses, and parasites, found in water sources like reservoirs, rivers, and groundwater. This process prevents the spread of numerous waterborne diseases such as cholera, typhoid fever, and giardiasis.
The practice of chlorination has significantly reduced outbreaks of waterborne diseases for over a century, making it a major advancement in public health. Water utilities add chlorine to raw water, at various points during treatment, and before distribution to maintain disinfection throughout the piping system. This ensures water remains safe as it travels from the treatment plant to consumers’ taps. Chlorine levels up to 4 milligrams per liter (mg/L), or 4 parts per million (ppm), are considered safe in drinking water.
Impacts on Human Health
Chlorinated water can impact human health through ingestion, external contact with skin and hair, and inhalation of vapors.
Ingestion
When chlorine reacts with organic matter naturally present in water, it can form disinfection byproducts (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs). Research into the long-term health concerns associated with these DBPs is ongoing. Some studies indicate potential links between long-term exposure to DBPs and certain cancers, including bladder cancer, as well as liver or kidney issues and reproductive problems. Regulatory guidelines are set to ensure a low level of potential health risk over a typical lifetime of exposure.
External Contact (Skin and Hair)
Chlorine can strip natural oils from skin and hair, leading to dryness, irritation, and sometimes exacerbating conditions like eczema or dermatitis. This can cause skin to become itchy, flaky, and red. For hair, chlorine can result in dryness, brittleness, and frizziness by lifting the hair cuticle. It can also affect hair color, potentially causing fading or a greenish tint, especially in lighter hair.
Inhalation (Vapors)
In enclosed spaces like showers, hot water vaporizes chlorine, allowing it to be inhaled. This can irritate the respiratory tract, potentially causing coughing, throat irritation, and shortness of breath. Individuals with pre-existing respiratory conditions such as asthma or bronchitis, as well as children and the elderly, may be more susceptible to these effects. Exposure to chlorine vapors during showering can be significant, potentially greater than exposure from drinking chlorinated water.
Other Effects: Aesthetic and Environmental Considerations
Beyond direct health impacts, chlorine in water also presents aesthetic and environmental considerations.
Aesthetic Effects
The presence of chlorine in tap water often results in a noticeable taste and odor, commonly described as a “bleach-like” smell or a chemical taste. This can affect the palatability of drinking water, making it less appealing to some individuals. The intensity of this taste and odor can vary depending on factors such as the initial chlorine concentration, water temperature, and the distance the water travels through pipes to the tap.
Environmental Effects
While chlorine plays a beneficial role in water treatment, its discharge into natural aquatic environments can be harmful to aquatic life. Chlorine and its reaction products are toxic to various aquatic organisms, including fish, invertebrates, and plants. Treated wastewater often undergoes dechlorination to remove residual chlorine before being released back into rivers or lakes, mitigating its potential environmental impact.
Strategies for Minimizing Exposure
For individuals concerned about chlorine exposure, several practical strategies can help minimize contact with chlorinated water. These methods aim to reduce exposure without compromising the essential disinfection process that keeps water safe.
Water filtration systems are effective tools for removing chlorine and its byproducts. Activated carbon filters, commonly found in pitcher filters, faucet-mounted filters, and whole-house systems, work by adsorbing chlorine and many DBPs as water passes through. Regular replacement of filter cartridges is important to maintain their effectiveness.
Boiling water can help dissipate some free chlorine, as chlorine is volatile and evaporates at higher temperatures. However, boiling is less effective for removing all DBPs and does not eliminate other chemical contaminants or heavy metals. Allowing water to sit in an open container for some time also permits chlorine to evaporate.
To reduce exposure during showering, specialized shower filters can be installed. These filters, often containing KDF (kinetic degradation fluxion) media and activated carbon, are designed to neutralize chlorine and reduce inhalation of chlorine vapors. Ensuring good ventilation in bathrooms by opening a window or using an exhaust fan can also help disperse airborne chlorine. Consumers can consult their local water utility’s annual water quality reports for specific information about their water supply and the disinfectants used.