Effectiveness of Disinfectants on Different Pathogens
Microorganism Reduction Ability
Disinfectant E. Coli Giardia Cryptosporidium Viruses
Chlorine Very effective Moderately effective Not effective Very effective
Ozone Very effective Very effective Very effective Very effective
Chloramines Very effective Moderately effective Not effective Moderately effective
Chlorine dioxide Very effective Moderately effective Moderately effective Very effective
Ultraviolet radiation Very effective Very effective Very effective Moderately effective

Note: The reduction levels in the table are for normal dose and contact time conditions; they are only for general comparison. The effectiveness of different disinfectants depends on the dose, contact time and water characteristics.

Many aquatics professionals are hearing reports about swim meets where athletes have to queue up in the hallway because the natatorium air is too polluted to breathe. Similarly, large indoor waterparks have become the topic du jour on the 5 o’clock news because scores of paying customers claim to have fallen ill from the air they were breathing during their visit to the facility.

The health issues relating to disinfection byproducts (DBPs) and indoor air contamination may soon overtake the concerns about recreational waterborne illnesses (RWIs). A strong case is being built, supported by studies, that many other things besides chloramines in pool water should concern us and that these compounds may cause illness.

First, a few definitions need to be clarified. The terms chloramines and combined chlorine are not interchangeable. “Chloramine” refers specifically to monochloramine, dichloramine and trichloramine, also called nitrogen trichloride. The term “combined chlorine” encompasses these three chloramine species plus myriad other chlorinated nitrogen compounds. The results of combined chlorine wet tests indicate the presence of many other substances in the water, not just chloramines.

Some of these chemicals or compounds that show up as combined chlorine may include oxidants such as potassium mono-persulfate and ozone. In the absence of these chemicals, the results of a combined chlorine test indicate the presence of synthetic organic compounds, volatile organic compounds and other higher chlorinated ammonia compounds called N-chloro compounds. Clearly, it is combined chlorine that we should be concerned about, not just chloramines. Many of these chlorinated compounds do not yield to breakpoint chlorination.

To complicate things further, it’s fair to say that pool water chemistry is very poorly understood. To date, there has not been a single comprehensive study performed on the multitude of chemical reactions that occur in a pool. Fortunately, many studies have been performed on the formation of DBPs in chlorinated drinking water supplies. By inference, we can assume that most, if not all, of the same reactions occur in pool water because we typically fill pools with potable water.

It may even be safe to say that a greater concentration of DBPs is formed in pool water because it contains more contaminants and a wider range of chemicals. The EPA has identified and qualified only an estimated 50 percent of the DBPs that form in chlorinated drinking water. This adds up to approximately 500 DBPs, most of which have not been qualified as to their impact on the health of swimmers. The EPA has identified hundreds of DBPs in potable water, and limited the allowable concentration there. No equivalent restrictions exist for pool water in the United States. (See the USEPA Web site at www.epa.gov/athens/research/process/drinkingwater.html for more details.)

Furthermore, we should not be solely concerned with DBPs that offgas a pool surface into the atmosphere. Consider for a moment the immense popularity of indoor waterparks with their plethora of sprays, geysers, falls and jets. These types of attractions aerosolize the pool water with its hundreds of identified and unidentified DBPs, pool chemicals and body deposits.

Unfortunately, each and every patron in the park inhales these minute water droplets. Many operators of indoor waterparks report air filters clogged with much more than dust. Some describe the deposits on their air filters as fatty oils and grease. The sources of these substances are the people in the pool. Not only are the air filters picking up these substances, but so, too, are the lungs of the people breathing in the air.

What can we do about it? A good place to start is modern building designs. While these structures are energy-efficient, indoor air quality has diminished. The tighter air envelope within the structure does not permit a building to “breathe.” Meanwhile, many new buildings feature HVAC equipment that is designed and installed to bring in very little fresh outside air. In the case of an indoor pool facility, this circulation of air contaminated with DBPs and other compounds exacerbates our problems.

Another point to consider is the design of new pools. It’s generally accepted that a surge tank in any filtration system collects the dirtiest water in the pool. In the case of spraypads, it is the only point of water collection. That means the turnover is significantly altered when feature pumps are turned on. In essence, water is short-cycled, resulting in unfiltered and untreated water becoming aerosolized into the atmosphere via the features, slides and sprays.

It may be time for codes to mandate that water for features come directly from the pool. In cases such as spraypads, where no other water sources exist, an additional filtrate tank that collects treated water should be required.

It’s also incumbent upon us to carefully consider the filter types, turnovers, outside air dilution, supplemental chloramine control equipment and systems controls we specify and install.

Exciting examples of new equipment are regenerative media filters; ultraviolet systems that not only provide an extra disinfection barrier but also DBP control, as demonstrated by the ground-breaking studies performed by Dr. Chip Blatchley and Dr. Jing Li of Purdue University; new HVAC system designs that are efficient, but allow for higher amounts of outside dilution air to be used in natatoriums; and control systems that harmonize the functions of chemical controllers, UV and HVAC systems, allowing the equipment to adjust as a complete package to accommodate changes in bather loading.

The term “value engineering” also should be re-evaluated. Too many times, a value-engineered project, while meeting budgetary constraints, results in “sick natatorium syndrome,” leading to more discomfort and illnesses.

Maybe it is time to re-examine how we treat pool water. Let’s look at the European model. As a general rule, their equipment selection is geared toward using the best available technologies and designs. Overall, the equipment for comparable pools is larger, turnover times are lower, bather capacities are lower, and operator training is more stringent.

It may even be time to think about how we use chlorine. Europeans understand that the more chlorine is added to a pool, the more DBPs will form. The German DIN standard limits the amount of free chlorine in a swimming pool to 0.6 mg/L (ppm) and a pH range of 6.5 to 7.6, which maximizes the formation of HOCl. Taking this concept further, it may be time to rethink the use of sodium hypochlorite and calcium hypochlorite completely and move to a different sanitizer/oxidizer such as chlorine dioxide.

Chlorine dioxide is more effective against most RWIs than chlorine is — especially in the case of cryptosporidium, as noted in the USEPA Guidance Manual for Alternative Disinfectants and Oxidants. It forms far fewer DBPs compared with chlorine and, based on recent toxicological studies mentioned in Chapter 12 of the Handbook of Chlorination by Clifford White, previous fears about chlorine dioxide’s principal byproduct — chlorite ion — have been allayed because of new generation techniques.

It is clear that we cannot continue with business as usual. We must ask ourselves the hard questions and take the bold steps necessary for the health of our industry and, more importantly, the health of our customers.