The familiar, pungent odor often described as a “chlorine smell” in water is common in both public swimming pools and tap water. This smell is frequently misunderstood, as it is rarely the scent of the primary disinfectant itself. Chlorine is used in water treatment systems and pools to eliminate disease-causing organisms. The substance you are smelling is actually a related compound that forms when this disinfectant interacts with contaminants.
Why You Are Smelling Chloramines, Not Chlorine
The effective form of chlorine used to sanitize water, known as “free chlorine,” is largely odorless at typical concentrations. The strong, irritating smell is instead caused by chemical byproducts called chloramines, or combined chlorine. Chloramines form when free chlorine bonds with nitrogen-containing organic matter introduced into the water supply.
This organic matter includes ammonia and nitrogen compounds found in human sweat, urine, body oils, and dirt. The reaction creates a series of compounds, including monochloramine, dichloramine, and trichloramine. The smell is predominantly attributed to the more volatile forms, particularly trichloramine, which readily off-gasses into the surrounding air.
The presence of chloramines indicates that the added chlorine has successfully reacted with and neutralized contaminants. However, once chlorine is bound in this way, it is less effective at further disinfection compared to free chlorine.
What the Presence of Chloramines Signifies
Detecting a distinct chlorine odor indicates a high concentration of combined chlorine compounds. Rather than signaling an excess of disinfectant, a strong smell suggests a significant level of organic contamination that has consumed the free chlorine. In swimming pools, the smell serves as a warning sign of poor water quality.
When this strong odor is present, the free chlorine residual has been largely converted into chloramines, reducing the water’s ability to kill new germs. The common belief that a strong smell means “too much chlorine” is often the opposite of the chemical reality; a properly sanitized supply should have a minimal odor.
In drinking water systems, utilities sometimes intentionally add chloramines because they are more stable than free chlorine and last longer as the water travels through pipes. This stability ensures a disinfecting residual remains present all the way to the consumer’s tap. However, even in tap water, an unusually strong smell may signal localized issues, such as a high concentration of organic matter in the supply or pipes.
Health Concerns and Removal Methods
Exposure to high levels of chloramines can cause irritation to the eyes, skin, and respiratory system. This is a common concern in indoor aquatic facilities, where trichloramine gas released from the water can accumulate without proper ventilation. Swimmers, staff, and spectators may experience symptoms such as eye redness, skin rashes, coughing, congestion, and the exacerbation of asthma.
The risk is low for chloraminated tap water that meets regulatory standards. However, individuals with sensitive skin or existing conditions like eczema may find that chloramine-treated water causes dryness or irritation. For those using home dialysis machines, the water must be specially filtered to remove chloramines before use, as they can cause serious blood issues.
Reducing Chloramines in Tap Water
For consumers seeking to reduce chloramines in their tap water, home filtration systems are the most effective solution. Standard activated carbon filters may reduce some chloramines, but specialized catalytic carbon filters are engineered to chemically break down the compounds with greater efficiency. Reverse osmosis systems are also highly effective at removing both chlorine and the ammonia component of chloramines. A simple, temporary method for reducing volatile chloramines is to let the water sit uncovered, though this is slow and less effective than for free chlorine.
Pool Shocking
For swimming pools, the solution to a strong odor is “shocking” or superchlorination. This involves adding a large dose of free chlorine to the water, which chemically breaks down the existing chloramines and restores the free chlorine level necessary for effective sanitation.