The Natatorium Puzzle: Five Warning Signs

When designing, improving, or maintaining a natatorium, you should start with the end users in mind, swimmers and other pool users or campus staff. While calculations, design guidelines, and aesthetics all matter, those pool users are the most important factor.

From the swim team-breathing hard after a strenuous practice-to the coaches, spectators, or casual swimmers, there are students and staff inside those natatoriums who will be breathing the air for hours at a time and month after month, if not year after year.

Every day I talk to pool operators, swim coaches, and owners. Oftentimes, they reach out to my office because they notice unhealthy symptoms but have not identified the problem yet. Here are a few of the most common things that they tell me. They may note concerns about that distinctive indoor pool smell, rusty pool equipment that was purchased only months ago, walls that seem to sweat, and breathing difficulties for student-athletes and staff.

Specific Concerns

First, they may note an “indoor pool smell,” though they often chalk that up to something normal because it’s been that way for years. They might note that they have rusty equipment, though it was only purchased the previous year. Perhaps they noticed that the windows and walls appear to be “sweating” or comment that it appears to be raining indoors. Even worse, they may say that their students have to use inhalers at swim practice. Finally, they may end with some version of this line: “I have x, so everything is fine.”

Let’s start with that last one. If you catch yourself saying this-that one product means everything is fine-it should serve as a bright red flag. Despite what some salesmen might tell you, there is no silver bullet that can fix every problem in your pool environment.

A natatorium is a complex environment that has to be maintained by a certified pool operator and other professionals. A well-balanced indoor pool environment will include systems and best practices to address not only water quality, but air quality, ventilation, dehumidification, structural issues, and patron/employee health as well. Here are some examples of what we mean:

Primary Disinfectant – Usually this is Chlorine, which can be delivered several ways, or Bromine. Chlorine delivery methods include CalHypo, Liquid Chlorine, and “Salt Water.” (Yes, “salt water” is actually just a chlorine delivery system). This is your first line of defense for water quality.

Secondary Disinfectant – UV, Ozone,Hydroxyl Radicals, etc. These systems are designed to eliminate any harmful organics left in the water.

Pool Filter – Sand, DE, Regenerative, Green Glass, etc. Filters keep water clean and clear.

Air Handling Units (AHU) – Regulate Outside Air (OSA) and exhaust, supplying air to the pool and returning it through the unit. Should meet ASHRAE standards.

Pool Dehumidification Units (PDU) -As the name suggests, units that balance humidity in the natatorium. Every PDU is an AHU, but not every AHU is a PDU.

Source Capture Exhaust – An add-on for the AHU, source capture exhaust removes the air with heaviest chloramine content from the facility directly. This can lead to better Indoor Air Quality (IAQ).

Airflow Pattern – Created and influenced by metal or fabric ductwork, floor supplies, diffusers, fans, return grilles, plenums, exhaust fans, and many more features.

Structural Concerns – Because natatoriums are infamously corrosive, metal and concrete structural elements should be examined regularly. “Stainless Steel” does not mean “Corrosion-proof Steel.”

The Indoor Pool Smell

On to the next warning sign: “That indoor pool smell has always been here.” Many of you, like me, grew up with this mentality. The fact of the matter is that this statement simply is not true. Most outdoor pools and some indoor pools do not have a problem with “pool smell” because they are properly ventilated.

That smell comes from harmful chloramine gasses that are normal byproducts of the disinfectants in the water. Water quality plays a role in “pool smell” as well. If these gasses are allowed to build up within the natatorium, the smell is just one of the negative effects.

If you can smell the pool, chloramine gasses are above the maximum safe level according to the World Aquatic Health Code. This can lead to problems such as burning eyes, respiratory distress, vomiting, and rusting/ corrosion of metal surfaces and equipment.

New, Yet Rusty Equipment

“I just bought this equipment a year ago and it’s already rusty.” That is what a Director of Facilities for a major university said to me last year. His first instinct was to blame the manufacturer of the PDU. We dug a little bit deeper and discovered that the facility was unintentionally designed to draw corrosive gasses from the pool area directly through the sensitive and vulnerable metal components in the PDU.

PDUs are very expensive and he was not happy that components needed to be replaced so quickly. He knew that a PDU should last 15+ years when properly designed and maintained. I visited the natatorium and conducted a study, identifying several underlying causes of the problem. The solution recommended for this facility was modification of existing ductwork and installation of source-capture exhaust. With purpose designed airflow pattern and source capture exhaust, rust and corrosion in PDUs and on deck equipment can be limited.

Poor Indoor Air Quality

One concerned coach that I spoke to said his athletes had to use inhalers at swim practice. He hated seeing the students suffer, of course, and would do anything in his power to help them breathe easier. Lifeguards at the same facility had respiratory problems as well, especially during peak activity hours.

Just above the surface of the water, within three inches, is where swimmers primarily breathe. Those same nasty chloramine gasses that we mentioned above are created in the water and, since they are heavier than air, remain just above the water’s surface.

More chloramine gasses are produced during periods of heavy activity and when pool water is disturbed. This means that swim practice and swim meets are usually the worst events for air quality. Research has shown that competitive swimmers have asthma rates four times higher than the general population. Other conditions such as “swimmer’s cough” and “lifeguard lung” are also associated with indoor swimming pools. It is not uncommon to attend swim practice at an indoor pool and find a line of inhalers along the side of the pool. Chloramine gasses irritate sensitive organs like eyes and lungs which researchers believe contributes to these medical conditions.

Indoor Rain: Sweating Walls and Windows

After speaking with a facility operator in Illinois, I wrote down his exact words: “It’s raining in here; the windows and walls sweat.” My first instinct was to investigate the PDU, and sure enough, the facility did not have one. They had no means of controlling the humidity level, and to make matters worse they had a very low percentage of OSA coming in.

We always recommend investing in a PDU, no matter what part of the country you are located in. There are a number of good, reputable dehumidification companies out there. We recommend choosing a manufacturer who specializes in pool dehumidification, rather than a commercial HVAC manufacturer. Pools are very specialized environments and PDUs are designed specifically for them.

A Warning Sign of Complacency

This brings us back around to the final consideration: If you find yourself with the “I have x, so everything is fine” approach, see this as what it is: a warning sign of complacency. To have a truly healthy and effective natatorium, several systems have to be working together with one another. Pools are a part of a very complicated environment in a natatorium. Trained professionals are needed to keep everything balanced correctly. There is no silver bullet; the only solution is to put in place and maintain the right pieces so that you can master the natatorium puzzle.

About the Author
Luke Beadle is a consultant for Paddock Pool Equipment Company in Rock Hill, SC. Paddock pioneered source capture exhaust technology and Luke primarily works with facilities across the country to find the right solutions for their IAQ concerns. Contact him at (803) 366-3822 or