The “chlorine smell” at an indoor pool comes from chloramines, which form when chlorine reacts with sweat, urine and other waste that swimmers bring into the water. To get rid of them, move fresh air across the water surface, pull contaminated air out where it collects at the water’s edge, and cut the amount of chloramines that form in the water in the first place.
Most facilities need all three. Ventilation removes chloramines after they reach the air, but it cannot stop them from forming, so the best results come from treating the air and the water together.
What causes the chlorine smell at an indoor pool?
The smell at an indoor pool is chloramines. CDC’s chloramines and pool operation guidance (2025) says chloramines are a type of combined chlorine that forms in the water when chlorine binds to the body waste swimmers bring in, and then off-gasses into the air above the water.
Salt water pools are not an exception. A salt system makes chlorine from the salt in the water, so a salt pool can produce chloramines and the same smell.
CDC also says chloramines that off-gas from the water are heavier than air and settle on top of the water’s surface. That is why the air right above the water, where swimmers breathe, is usually the worst air in the building.
Why does poor indoor pool air quality matter?
Chloramines in the air irritate the skin, eyes and respiratory tract, including the nose, according to CDC’s 2025 guidance, and they create an unhealthy environment for swimmers, spectators and staff. Lifeguards and other staff breathe that air for whole shifts.
Two CDC reports show how quickly this becomes a staff health problem:
- Ohio, 2007: at a hotel indoor waterpark, the local health district received 665 reports of respiratory and eye irritation from patrons and lifeguards between January and March 2007. CDC’s MMWR report (2009) found that insufficient air movement and distribution likely led to chloramines building up, and after the facility moved its air supply and return ducts closer to the pool deck, no new cases were reported.
- Ohio, 2016: at another indoor waterpark resort, employees were about four times more likely to have work-related eye and respiratory symptoms, according to a 2017 MMWR report. Investigators found the fans of five of the waterpark’s six HVAC units were not working.
For more on the health research, see why so many elite swimmers have asthma.
How much ventilation does an indoor pool need?
ASHRAE Standard 62.1 sets a minimum outdoor air rate of 0.48 cfm per square foot of pool and deck area, as described in a July 2017 ASHRAE Journal article on ventilation requirements for indoor pools (which cites the 2016 edition of the standard). The article’s authors, who work for an HVAC equipment maker, note that the standard’s minimum rates may not always produce acceptable air quality on their own. Check the edition of ASHRAE 62.1 and the health code that apply to your facility.
Where the air goes matters as much as how much air comes in. CDC’s 2025 guidance says to set up the HVAC system to move fresh air across the water’s surface and to exhaust chloramine-polluted air outside. A 2025 NACCHO quick guide to managing chloramines, based on the 2024 Model Aquatic Health Code, says indoor pools must keep a continuous flow of fresh air just above the water surface.
Bringing in more outdoor air also has a cost. Every extra cubic foot of outdoor air has to be heated or cooled and dehumidified, so facilities that rely on ventilation alone often end up paying for a lot of air to handle a problem that starts in the water.
What is source capture for indoor pool air?
Source capture pulls contaminated air out at the point where chloramines collect, just above the water, instead of mixing it into the whole room. The 2017 ASHRAE Journal article describes source capture as a system with multiple exhaust points in the water-level pool gutter, and says it should, in theory, remove a higher concentration of chloramines. It also recommends placing return air inlets low to capture chloramines off the pool surface.
Some facilities add a dedicated deck-level or gutter-level exhaust product, such as Paddock’s Evacuator, to do this. Source capture removes chloramines faster once they reach the air, but like ventilation it does not stop them from forming.
How do you reduce chloramines in the pool water?
Cut chloramines at the source by keeping waste out of the water and breaking down what gets in. CDC’s 2025 guidance recommends:
- Rinse before swimming: require swimmers and staff to rinse off before getting into the water, and remind swimmers to use the restroom.
- Watch combined chlorine: CDC says most health departments limit combined chlorine to 0.4 ppm or less. The 2024 Model Aquatic Health Code sets the same limit (section 5.7.4.4.2, per the NACCHO guide).
- Break down chloramines that form: CDC lists raising the free chlorine level to 10 times the combined chlorine level, and using ultraviolet light or ozone systems to break down chloramines in the water.
Our post on what chloramines are and how to reduce them covers the water chemistry in more detail.
How does hydroxyl-based AOP help with indoor pool air?
A Clear Comfort hydroxyl-based AOP system is a supplemental system that adds hydroxyl-based oxidation to the water in the return line. It breaks down the contaminants that react with chlorine to form chloramines and other disinfection byproducts, so fewer of them reach the air. It works alongside a low chlorine residual, which is still needed, and alongside the facility’s ventilation.
In Clear Comfort’s commercial case studies, facilities have reduced chloramines and other disinfection byproducts by 50% to 90%. Results vary by site, bather load and how the facility runs its ventilation and chemistry. For example, in a 2017 to 2018 comparison case study at two similar high-use indoor facilities in Southern California, water samples sent to an independent lab showed Clear Comfort AOP removed 94% of haloacetic acids (HAAs), a group of disinfection byproducts, compared with 83% for medium-pressure UV. That study measured byproducts in the water, not chloramines in the air.
Hydroxyl-based AOP also adds protection against chlorine-resistant germs. In a 2014 University of Colorado Boulder lab study of the Clear Comfort system, Crypto was reduced by up to 99.99% (4-log) by the 60-minute sample, in lab test water. Learn more about Clear Comfort for aquatic facilities.
Why combine ventilation, source capture and water treatment?
Each approach handles a different part of the problem. Ventilation dilutes and removes chloramines in the room, source capture removes them where they collect at the water’s surface, and water treatment, from rinse showers to supplemental systems, reduces how many form in the first place.
A practical plan for most indoor facilities:
- Check that the HVAC system moves fresh air across the water surface and exhausts it outside, and that every fan and damper works.
- Test combined chlorine every day and act when it rises above 0.4 ppm.
- Require pre-swim rinsing and post clear signs about it.
- Consider source capture at the gutter or deck level if odor complaints continue.
- Add a supplemental system, such as UV, ozone or hydroxyl-based AOP, to break down the contaminants that form chloramines.
Frequently asked questions
How do I get rid of chloramines and chlorine smell at an indoor pool?
Move fresh air across the water surface and exhaust it outside, keep combined chlorine at or below 0.4 ppm, require swimmers to rinse off before they swim, and use a supplemental system such as UV, ozone or hydroxyl-based AOP to break down chloramines in the water. CDC’s 2025 operator guidance recommends each of these steps.
What causes the chlorine smell at indoor pools?
The smell comes from chloramines, which form when chlorine reacts with sweat, urine and other waste from swimmers. CDC says chloramines off-gas from the water, are heavier than air and settle just above the water’s surface.
Is indoor pool air bad for lifeguards and staff?
It can be when chloramines build up. CDC says chloramines irritate the eyes, skin and respiratory tract, and a 2017 CDC report found employees at an Ohio indoor waterpark were about four times more likely to have work-related eye and respiratory symptoms when most of its HVAC fans were not working.
How much ventilation does an indoor pool need?
ASHRAE Standard 62.1 sets a minimum outdoor air rate of 0.48 cfm per square foot of pool and deck area. Where the air moves matters too: CDC recommends moving fresh air across the water’s surface and exhausting chloramine-polluted air outside.
What combined chlorine level is too high for a pool?
CDC says most health departments limit combined chlorine to 0.4 ppm or less, and the 2024 Model Aquatic Health Code uses the same limit. A higher reading means chloramines are building up and the operator should act.
Does UV or AOP reduce chloramines in pool air?
They reduce chloramines in the water, which means fewer reach the air. CDC lists UV and ozone systems as ways to break down chloramines, and Clear Comfort’s commercial case studies show 50% to 90% reductions in chloramines and other disinfection byproducts, depending on the site.
Want fresher air at your facility? See how Clear Comfort works for aquatic facilities.
Zach Morris
VP of Customer Success
Gabrielle Palumbo
Marketing Director
