Most municipal water supplies contain chlorine, or a chlorine-based compound, and this disinfectant is therefore present in the water used for showering. This practice is a public health measure to ensure water safety, but it introduces a chemical that interacts with the warm, enclosed environment of a bathroom. The presence of chlorine in shower water is a certainty for most consumers connected to a public water system.
Why Chlorine is in Tap Water
Chlorine is introduced into public water systems at the treatment plant to destroy harmful microorganisms that can cause waterborne diseases. This chemical compound is highly effective at neutralizing bacteria, viruses, and protozoa. Water utilities must maintain a Disinfectant Residual, which is a measurable level of chlorine that remains active in the water after the initial treatment.
This residual is necessary to prevent microbial growth and contamination as the water travels through the distribution system to reach the consumer’s tap. Some systems use free chlorine, which is a highly reactive form, while others employ chloramines, a compound of chlorine and ammonia. Chloramines are less potent but are more stable and persistent, allowing the residual to last longer in extensive distribution networks.
How Showering Increases Exposure
Showering significantly increases exposure to chlorine. The primary mechanism for this increased exposure is volatilization, the rapid conversion of a substance from its liquid state to a gaseous state. When shower water is heated, the chlorine molecules detach from the water at a much faster rate than the water itself, concentrating the chemical in the surrounding air.
This concentrated chlorine gas becomes part of the steam and is then inhaled directly into the lungs. The respiratory route of exposure is considered a more direct pathway into the bloodstream than ingestion, which is why showering can lead to a higher overall exposure than drinking the same water. The warm water also causes skin pores to open, which facilitates dermal absorption of chlorine directly from the water spray.
Health and Aesthetic Effects of Exposure
Exposure to chlorine and its byproducts during a hot shower impacts both the appearance and the internal health of the body. Chlorine strips the skin of its natural protective oils, leading to dryness, flakiness, and the potential exacerbation of pre-existing conditions like eczema and psoriasis.
For hair, this loss of natural oil can cause the strands to become dry, brittle, and prone to breakage. It also contributes to the fading of chemically treated hair color by oxidizing the dye molecules. Beyond these aesthetic concerns, the inhalation of chlorine gas and its reaction byproducts poses a more direct health risk to the respiratory system.
Inhaled chlorine vapor can irritate the mucous membranes of the nose, throat, and bronchial passages, which may trigger asthma attacks or worsen chronic respiratory conditions. Furthermore, when chlorine reacts with organic matter in the water, it forms toxic Disinfection Byproducts (DBPs), the most common of which are trihalomethanes (THMs). These compounds are highly volatile. Exposure to THMs has been associated with various health concerns, including potential links to certain cancers.
Methods for Reducing Chlorine Exposure
Several solutions exist to mitigate exposure to chlorine and its byproducts during showering. The most common and effective method is installing a dedicated showerhead filter, which is designed to remove chlorine at the point of use. These filters employ specialized media to neutralize or remove the disinfectant before the water hits your skin.
Activated carbon is a filter medium, but it loses effectiveness rapidly in high temperatures. A more effective solution for hot water is Kinetic Degradation Fluxion (KDF) media, which uses a redox (reduction-oxidation) process to convert free chlorine into a harmless chloride. Calcium sulfite is another media often used in conjunction with KDF, as it is highly effective at neutralizing both chlorine and chloramines in hot water. In addition to filtration, simply ensuring the bathroom is well-ventilated, such as by running the exhaust fan, helps remove the concentrated chlorine gas and volatile disinfection byproducts from the air.