If you’ve ever stepped into a public indoor pool and immediately caught a pungent “chlorine smell,” you might have thought it was just a heavy dose of chlorine. Surprisingly, that sharp, irritating odor is not caused by chlorine itself—but by something else entirely. In fact, that strong swimming pool water smell is often a sign of improper pool chemistry and can point to health and comfort issues for swimmers. Understanding the science behind the smell can help both pool owners and users recognize when pool maintenance is lacking and how it might be impacting air and water quality.
In this comprehensive article, we’ll break down the chemistry and causes behind the odor in swimming pool water, explain how it affects swimmers, and provide practical advice on how to reduce or eliminate the smell.
The Real Source of the Smell: Chloramines
When most people think of pool smells, they immediately think of chlorine—but in reality, the most pungent odors in pool water come from chloramines, not free chlorine. Chloramines are chemical compounds formed when chlorine-based disinfectants react with nitrogen-containing substances introduced into the pool by swimmers.
How Chloramines Form in Pool Water
Chlorine is used to disinfect water by oxidizing and killing harmful bacteria and pathogens. However, when chlorine mixes with contaminants like:
- Sweat
- Urine
- Saliva
- Body oils
- Cosmetics or lotions
…it forms chloramines. Common chloramines include monochloramine, dichloramine, and trichloramine, with trichloramine being the most volatile and responsible for that sharp, chemical smell.
Degradation of Chlorine Efficiency
When chlorine binds with these contaminants to form chloramines, its disinfecting power is greatly reduced. That means while the water may smell like chlorine, it’s actually not as clean or sanitized as it should be. Over time, the chlorine demand increases, and the concentration of chloramines rises—especially in pools with poor circulation and insufficient ventilation.
The Health and Comfort Impacts of Chloramines
The presence of chloramines isn’t just an aesthetic issue—it can lead to discomfort and even health problems for regular pool users.
Respiratory Irritation
One of the most common effects of chloramine exposure is respiratory irritation. Trichloramine, in particular, can become airborne when pool water is agitated (such as with splashing or when a pool uses waterfalls or jets). Inhaling these chloramines can lead to:
- Coughing
- Wheezing
- Shortness of breath
- Aggravation of asthma symptoms
This is a serious concern for indoor pools where ventilation is often limited. Swimmers, lifeguards, and staff who spend long hours indoors may experience chronic respiratory issues.
Eye Irritation and Redness
A burning or stinging sensation in the eyes is a classic sign of chloramine exposure. Due to their volatility, chloramines can easily evaporate from water and irritate the mucous membranes. This phenomenon often leads swimmers to mistakenly believe their eyes are red because there’s “too much chlorine”—when in reality, the chlorine levels are low and the chloramine levels are high.
Skin Irritation and Dryness
High chloramine levels can also contribute to skin dryness, itchiness, or rash-like symptoms, particularly in swimmers with sensitive skin or underlying skin conditions like eczema. Prolonged exposure may worsen these symptoms.
Why Indoor Pools Are More Affected
While chloramines are present in both indoor and outdoor pools, they tend to build up more significantly in indoor facilities due to several environmental factors.
Lack of Proper Ventilation
Indoor pools often have limited airflow, which prevents chloramines from escaping into the atmosphere. Instead, they accumulate around the pool deck and the breathing zone where swimmers and staff are most exposed. Without adequate ventilation systems, the chemical smell becomes more concentrated and persistent.
High Bather Load and Contaminants
Indoor pools are typically used year-round and often have a high turnover of swimmers. This results in more contaminants like sweat and urine being introduced into the water, which increases the formation of chloramines. Commercial pools and swim schools commonly see heavier bather loads, especially from children, which contributes significantly to the problem.
Lower UV Exposure
Sunlight naturally helps break down chloramines through ultraviolet (UV) radiation. Since indoor pools lack sunlight, this natural cleansing effect does not occur. That means indoor pool operators must rely more heavily on mechanical or chemical methods to manage chloramine buildup.
How Pool Operators Can Reduce Chloramines and Maintain Odor-Free Water
Pool owners and maintenance staff play a crucial role in managing pool chemistry to prevent chloramine buildup and maintain a pleasant swimming environment.
Regular Testing and Adjustment of Disinfectant Levels
Maintaining proper free chlorine levels is essential to control chloramine formation. The recommended level of free chlorine is typically between 1.0–3.0 ppm (parts per million) in most pools. Testing for:
- Free Chlorine (FC)
- Combined Chlorine (CC)
- pH
- Total Alkalinity
- Cyanuric Acid (stabilizer)
…helps pool technicians adjust chemical levels effectively and restore water purity.
Shock Treatment: Breaking Down Chloramines
To reduce chloramines, a process known as shocking the pool is used. This involves adding a large dose of chlorine (often in the form of calcium hypochlorite or sodium hypochlorite) to destroy the chloramine layer and restore sanitization.
Shock treatment should be conducted regularly—especially after peak usage hours like swim meets or crowded weekends. For indoor pools, pool staff may perform shocking during non-business hours to allow time for the strong chemical odor to subside.
Secondary Disinfection Systems
Many modern pools now use secondary sanitization systems such as:
| System | Function |
|---|---|
| UV Systems | Use ultraviolet light to break down chloramines and kill pathogens effectively |
| Ozone Generators | Inject ozone gas into the water to oxidize bacteria and chloramines |
| Mineral Water Purifiers | Use minerals like copper and silver to assist in killing bacteria and reducing chemical usage |
These systems can drastically improve air and water quality in indoor pools by supporting chlorine’s role and reducing reliance on chemical treatments alone.
Proper Ventilation and Air Circulation
Ensuring that an indoor pool area has effective HVAC (heating, ventilation, and air conditioning) systems is vital for reducing airborne chloramine concentration. Proper air turnover and chemical fume removal not only improve comfort but also protect the health of both patrons and staff.
What Swimmers Can Do to Help Prevent Odors
While pool operators have the primary responsibility for maintaining proper water chemistry, swimmers also play an essential role in reducing the factors that lead to chloramine buildup.
Shower Before Entering the Pool
Taking a quick pre-swim shower with soap removes much of the body oils, sweat, and other contaminants that contribute to chloramine formation. Encouraging all swimmers—especially children—to shower thoroughly before entering the water helps maintain better water quality and reduces chemical demand.
Avoid Using Heavy Lotions or Oils Before Swimming
Body lotions, sunscreens, and oils can significantly increase contaminant levels in the water. Even water-resistant sunscreen should be applied and allowed time to dry before entering a pool to prevent excessive transfer.
Use the Restroom Before Swimming
Urine is one of the primary contributors to chloramine formation. Parents should be encouraged to regularly check swim diapers and ensure young children use the restroom before entering the pool. Adults should also avoid urinating in the pool.
Myths About the Smell of Pool Water
Despite growing awareness about pool chemistry, several myths persist around the smell of swimming pool water.
Myth: “A Strong Chlorine Smell Means the Pool is Clean”
In reality, the opposite is true. A strong, acrid smell is often a sign that the water is contaminated and that disinfectant power has been greatly reduced due to chloramine buildup.
Myth: “Chlorine Causes Red Eyes”
As previously discussed, red and irritated eyes are more commonly linked to chloramines than chlorine. If eye irritation is frequent in a pool, it’s a sign that maintenance practices need closer attention.
Myth: “More Chlorine Always Leads to Cleaner Water”
Adding more chlorine without addressing combined chlorine levels or the source of contamination (e.g., swimmer hygiene, cleaning frequency) can actually worsen chloramine formation. It’s about using chlorine effectively—not excessively.
Maintaining Enjoyable Swimming Experiences
Ultimately, maintaining a pleasant and healthy pool environment is everyone’s responsibility—operators and users alike. Chloramines are a direct result of how people interact with the water, and the degree to which pool water is maintained. Understanding the connection between odor, contamination, and improper chemistry empowers both pool staff and patrons to make smarter decisions that benefit their experience, comfort, and long-term health.
Education and Awareness Are Key
Pool facilities should educate swimmers about the effects of poor hygiene practices and provide clear guidelines for entry. Visual signs, digital displays, or announcements before swim sessions can serve as effective reminders to shower before swimming and avoid contaminating the pool with unnecessary chemicals.
Technology and Innovation Are Helping
Modern advancements in water testing, filtration, and sanitation offer pool owners better tools than ever before to manage chloramines and deliver a safer, more pleasant swimming environment. Investing in these systems not only helps reduce chemical odors but improves the overall guest experience.
Conclusion
The strong odor commonly associated with swimming pool water is not due to chlorine itself, but rather the chemical byproducts known as chloramines—formed when chlorine reacts with organic contaminants. This chemical imbalance affects swimmer comfort, poses potential health risks, and signals underlying maintenance issues in the pool.
By understanding the science behind the smell and taking proactive steps—both through improved pool management and individual swimmer behavior—we can all contribute to a cleaner, healthier, and more enjoyable swimming experience. Whether you’re a pool operator, a regular swimmer, or a casual visitor, a well-maintained pool means crystal-clear water, minimal odor, and a safer environment for everyone.
Takeaways:
- The strong pool odor is from chloramines, not chlorine.
- Chloramines form when chlorine meets contaminants like sweat and urine.
- Poor ventilation and high bather loads increase the problem in indoor pools.
- Shock treatments and proper management of free chlorine help.
- Swimmers should shower before pools and avoid urinating in the water.
Why does swimming pool water have a strong odor?
The strong odor often associated with swimming pools is usually not caused by chlorine itself, but by a group of chemical compounds called chloramines. Chloramines form when chlorine disinfectants react with ammonia and other nitrogen-containing substances introduced into the water by swimmers—such as sweat, urine, and skin oils. These compounds are responsible for that characteristic “pool smell” that many people wrongly attribute to high chlorine levels. In fact, a strong odor can indicate that the chlorine is already overburdened and in need of replenishment or shocking.
To reduce this odor, pool operators must maintain proper chlorine levels and conduct regular “shock treatments” to break down chloramines and restore the effectiveness of the chlorine. Additionally, encouraging swimmers to shower before entering the pool and to avoid urinating in the water can significantly reduce the presence of organic contaminants. Well-maintained pool chemistry not only eliminates unpleasant odors but also ensures a safer and more comfortable swimming experience for everyone.
What are chloramines and how do they form in swimming pools?
Chloramines are chemical compounds formed when chlorine, used as a disinfectant in swimming pools, reacts with nitrogen-containing substances such as ammonia, urea, and other organic waste introduced by swimmers. These substances originate from sweat, urine, cosmetics, and even lotions that people bring into the pool. There are different types of chloramines—monochloramine, dichloramine, and trichloramine—each with varying levels of volatility and odor intensity. Trichloramine, in particular, is known for producing a strong, unpleasant smell and irritating effects on the eyes and respiratory system.
The formation of chloramines reduces the effectiveness of chlorine in killing bacteria and other pathogens. If not properly managed, chloramines can accumulate and lead to poor water quality and health concerns. To counteract their buildup, pool operators must regularly test the water for chloramine levels and apply oxidation techniques, such as superchlorination or the use of ultraviolet (UV) or ozone systems, to break down these compounds and restore chlorine’s sanitizing power.
Is the odor in pool water harmful to swimmers?
The odor itself from chloramines is not harmful in the traditional sense, but it can serve as an indicator of unhealthy water conditions. High levels of chloramines can cause irritation to the eyes, skin, and respiratory tract, particularly in enclosed or poorly ventilated pool areas such as indoor pools. Sensitive individuals, including those with asthma, may experience symptoms like coughing, wheezing, or itchy eyes in environments where chloramine concentration is elevated. Therefore, while the smell is often the first warning sign, it should not be ignored as a potential health hazard.
To create a safer swimming environment, it’s important to monitor and manage chloramine levels regularly. This includes maintaining appropriate free chlorine levels, improving air circulation in indoor pool facilities, and utilizing secondary treatment systems such as UV or ozone purification. Encouraging swimmer hygiene—like showering before entering the pool and avoiding urination in the water—also goes a long way in minimizing chloramine formation and protecting swimmer health.
How can you tell if pool water is properly chlorinated?
Properly chlorinated pool water typically does not have a strong chemical smell and does not cause noticeable irritation to the eyes or skin. A well-maintained pool should have a faint chlorine scent, if any, indicating the presence of “free chlorine” that is available to disinfect contaminants. Regular water testing should show a balance of free chlorine (usually between 1–3 ppm) and a low level of combined chlorine, which is a measure of chloramines. Water clarity and the absence of visible algae are additional signs that the chlorine system is functioning effectively.
Swimming pool operators can use test kits or digital meters to measure chlorine levels and pH balance, both of which are crucial for chlorine’s disinfecting capabilities. In addition to chemical testing, observing how swimmers react to the water can offer clues; if they leave the pool with red eyes or a strong smell clinging to their skin and hair, chloramines may have built up. To maintain proper chlorination, regular shocking and backwashing, along with monitoring bather load and encouraging good hygiene, are essential steps.
How do you reduce or eliminate the odor in swimming pool water?
To reduce or eliminate the strong odor in swimming pool water, the most effective method is to perform a “shock treatment” using a chlorine-based or non-chlorine shock oxidizer. This process breaks down chloramines and converts them into inactive compounds, restoring the effectiveness of chlorine in the pool. Regular shocking—especially after heavy swimmer usage—is essential to maintain clean and odor-free water. In addition, adjusting the pH of the pool water to the recommended range (7.2–7.8) helps chlorine work more efficiently, reducing the need for frequent shocks and minimizing odor.
Beyond chemical interventions, educating swimmers about proper hygiene can significantly reduce the problem at its source. Encouraging pre-swim showers, using swimwear that minimizes the absorption of contaminants, and discouraging urination in the pool all contribute to a cleaner aquatic environment. Pool operators can also install advanced systems such as UV or ozone generators to supplement chlorine and break down chloramines more continuously. These combined efforts can dramatically cut down on pool odor and improve overall swimmer comfort and safety.
Can the pool odor affect people who are not swimming?
Yes, the strong odor commonly found around swimming pools—particularly indoors—can affect people who are not actively in the water. The volatile chloramines responsible for the smell can evaporate into the air, causing respiratory irritation for spectators, lifeguards, and pool staff. In environments with poor ventilation, these airborne chloramines can accumulate and lead to symptoms such as coughing, sneezing, throat irritation, or even asthma attacks, especially in sensitive individuals. Children and the elderly may be more vulnerable to these effects, making air quality around pools a serious consideration.
To mitigate this, indoor pools should be equipped with effective ventilation and air circulation systems that help remove chloramine-laden air and replace it with fresh or filtered air. In addition, implementing water treatment systems that reduce chloramines—such as UV sterilizers or ozone generators—can significantly improve both water and air quality. Encouraging swimmers to observe hygiene practices, coupled with regular water testing and maintenance, can help ensure a safer and more pleasant experience for all individuals around the pool area.
Are there alternatives to chlorine that can prevent the odor problem?
Yes, there are alternative water treatment methods designed to reduce or eliminate the problems associated with chloramines and chlorine-based disinfection. One common option is the use of bromine, which is especially popular in spas and hot tubs due to its stability at high temperatures. While bromine can also produce some odor, it tends to be milder and less irritating than chlorine. Other alternatives include biguanide-based sanitizers, which do not produce chloramines or strong odors, but they require a completely different system of water maintenance, with different algaecides and filters.
Another approach involves using secondary disinfection systems like ultraviolet (UV) light or ozone generators in combination with chlorine. These systems actively break down chloramines and other contaminants before they can accumulate in the water, thereby reducing odor and irritation. Saltwater chlorine generators are also an option; they produce chlorine through electrolysis, which can lead to a more stable supply of disinfectant and potentially fewer odor issues. While these alternatives can minimize unpleasant smells, they still require proper maintenance and monitoring for safe and effective pool operation.