When entering a swimming pool, many people often notice a distinct odor that they commonly associate with chlorine. This familiar scent, present in both public and private swimming environments, is frequently perceived as an indicator of a clean and well-sanitized pool.
The Chemical Culprit
The familiar “chlorine smell” in swimming pools is not primarily due to the chlorine itself, but rather to chemical compounds known as chloramines. Chloramines (also known as combined chlorine) form when chlorine reacts with nitrogen-containing substances in the water. Pure chlorine, at typical pool concentrations, has a milder odor; the pungent scent is a byproduct of these interactions.
How Chloramines Form
Chloramines develop from specific chemical reactions involving chlorine and nitrogen compounds in pool water. Chlorine, often as hypochlorous acid, combines with ammonia or other nitrogenous organic materials to produce chloramines. These nitrogenous substances primarily originate from swimmers, including sweat, urine, skin cells, cosmetics, and other personal care products.
Different types of chloramines can form: monochloramine, dichloramine, and trichloramine. While monochloramine can function as a disinfectant, dichloramine and especially trichloramine cause strong, irritating odors. Trichloramines are volatile, readily becoming airborne and contributing significantly to the smell above the water surface.
What the Smell Indicates
A strong “chlorine smell” in a pool actually signals compromised water quality, rather than proper sanitation. This odor indicates that chloramines have accumulated in the water, often because there is insufficient active chlorine to break them down effectively. The presence of chloramines suggests the pool’s disinfection system may be overwhelmed by organic loads.
These elevated chloramine levels can lead to various irritations for swimmers and those nearby. Common effects include red, stinging eyes, itchy skin, and respiratory discomfort such as coughing, chest tightness, or wheezing. Chloramines are also less effective as disinfectants compared to free chlorine, making the water less capable of killing germs. High chloramine concentrations can corrode pool equipment and building materials, particularly in indoor settings.
Managing the Smell and Its Sources
Controlling the “chlorine smell” involves proactive pool maintenance and swimmer hygiene. A primary method for reducing chloramines is “shocking” the pool (superchlorination or breakpoint chlorination). This process involves adding a concentrated dose of chlorine to break down chloramines and other contaminants. For effective removal, the free chlorine level should typically be raised to about ten times the combined chlorine level.
Maintaining proper pH levels is also important, as pH influences chlorine’s effectiveness. Swimmer hygiene plays a significant role in preventing chloramine formation. Encouraging swimmers to shower with soap before entering helps remove organic matter like sweat, oils, and cosmetics. Avoiding urination in the pool also reduces the introduction of nitrogenous compounds. In indoor pools, proper ventilation exhausts airborne chloramines and introduces fresh air, improving air quality and reducing irritation.