Chloramines and Pool Operation

Key points

Chlorine is used at aquatic venues to kill germs, but when it binds to the body waste swimmers bring into pools, it can form chemicals called chloramines. Chloramines in the water irritate skin, eyes, and the respiratory tract (including the nose) when they turn into gas into the air above the water, particularly indoors. In addition, chloramines can also contribute to corrosion of metals around the aquatic venue and in air handling systems.

Close up of a pool lane at an indoor pool.

Overview of chloramines and what causes them

Chloramines are a type of combined chlorine that form in water and then off gas into the air above the water. Most city, county, and state health departments limit the amount of combined chlorine in the water to 0.4 ppm or less.

Chloramines can build up in the water, which means they can build up in the air if there is not enough fresh air surrounding pools and other places people swim in chlorinated water. This is particularly true for indoor aquatic facilities where air handling systems are not bringing in enough fresh air and exhausting enough chloramine-polluted air, which is common during winter months when heating costs increase. Chloramines that off gas from the water are heavier than air. This means they settle on top of the water's surface where they can cause negative health effects in swimmers and spectators.

Three things cause the buildup of chloramines in the air:

  • Disturbing the water's surface (for example, when swimmers move in the water or the water is sprayed through aquatic features),
  • Limiting movement of fresh air over the water's surface, and
  • Using air handling systems to limit the amount of fresh air brought into the swimming area and limit the amount of air polluted with chloramines exhausted out of the swimming area. This is common during winter months when heating costs are high.

Air handling systems might remove moisture from the air, but they don’t necessarily bring in enough fresh air or exhaust enough chloramine-polluted air. Pool operators need to consult with technical representatives on how to maximize the use of their air handling system to reduce chloramine accumulation while keeping heating costs down. If chloramines are not exhausted to the outside, the recirculated air flowing over the water can become loaded with chloramines. If the air surrounding the water is full of chloramines, chloramines can’t off gas in the surrounding air. This means chloramines will build up in the water and cause health effects in the swimmers.

How to prevent or remove chloramines

Stop pee, poop, dirt, and sweat from entering the water

  • Post signs or posters in the locker room that encourage swimmers and staff to:
    • Not enter the water when they have diarrhea
    • Use the toilet before getting into the water
    • Wear a bathing cap while in the water
    • Not pee or poop in the water.
  • Require swimmers and staff to rinse off before getting into the water—in other words, swimmers and staff should be wet before they get into the water. Even a quick rinse shower removes much of the body waste that helps form chloramines.
  • Be on alert for poop in the water; the distinctive chloramine odor in the swimming area; and respiratory, eye, or skin irritation in swimmers and staff in the swimming area.

Ensure adequate airflow in the swimming area

  • Set up the heating, ventilation, and air conditioning (HVAC) system to move fresh air across the water's surface and towards air exhaust vents to prevent the buildup of chloramines on top of the water's surface.
  • Exhaust air polluted with chloramines from the swimming area to the outside.
  • Bring fresh air from the outside into the swimming area. If the fresh air is cold, this will increase heating costs, but the cost of patron discomfort and illness linked to chloramines can be higher.

Monitor combined chlorine levels in the water and treat the water, as needed

  • Calculate the level of combined chlorine.
    • Measure the amount of total chlorine in the water.
    • Measure the amount of free chlorine in the water.
    • Subtract the free chlorine number from the total chlorine number: combined chlorine = total chlorine – free chlorine
  • Get rid of chloramines in the water, especially when the combined chlorine level is too high (for example, more than 0.4 ppm) by superchlorinating to off gas chloramines from the water and to convert them to nitrogen gas.
    • Close the pool to swimmers.
    • Make sure the swimming area is well-ventilated, because superchlorination (also known as "breakpoint chlorination") causes off gassing of the chloramines and creates nitrogen gas.
    • Raise the free chlorine level to 10 times the combined chlorine level.
    • Bring the free chlorine level back down to the required operating range.
  • Break down chloramines in the water, using ultraviolet light or ozone systems, which are also known to kill Cryptosporidium.