Problem Solver - August 2010
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Protecting Pool Patrons From RWIs


athers need to be kept safe, and pool operators also want to make the experience as pleasant as possible, while balancing the commercial needs of the business. Traditionally, chemicals such as chlorine have been added to pools to disinfect. This has worked well, but organisms have started to develop resistance to chlorine. In addition, the byproducts formed by the addition of chlorine to pool water can cause corrosion and are increasingly linked to asthma in children and elite athletes.

Q: What should we know about the risk of infection?

A: People swimming in pools, using splash pads or visiting waterparks are at risk from waterborne infection. Many of these infectious agents, which may be naturally present on bathers themselves and can be transmitted via pool water and surfaces, are developing increased resistance to chlorine. Some, such as cryptosporidium and giardia, have developed complete resistance to chlorine.

The adoption of UV light can help protect patrons as these problems grow. This should not be seen as a replacement for chlorine or good pool hygiene practices. The UV systems serve a dual role: primary disinfection of the waterborne organism and effective photolysis of the combined chlorine species.

Q: What is combined chlorine, and why should we be concerned about it?

A: The strong, acrid chlorine smell associated with swimming pools and spas is actually the combination of chlorine with compounds introduced into the pool, such as urine, sweat, hair, suntan oil and other organic compounds. These react with chlorine to form chloramines and other chemicals. Many research groups have studied the effects of exposure to these chemicals, notably finding an increased risk of asthma in pool workers, school children, elite athletes and others.

Air treatment systems can play a role in reducing the transmission of chloramines, but this approach is not a root-cause solution. UV systems can both disinfect pool water and also break up or photolyse the combined chlorine.

Q: How does UV light help?

A: UV light has the ability to destroy the cross bonds in the DNA contained in the nucleus of an organism, or RNA in the case of a virus. Technically, the organism is not killed by the UV light, but the damage caused to the DNA denies basic cell functions of replication, respiration and assimilation of food. Without these functions, the organism quickly dies.

It is important to note that medium-pressure UV light is required, as a number of researchers have shown that organisms exposed to a comparable dose of UV light from a low-pressure lamp are able to repair the damage to their DNA.

In addition to fighting infectious agents, wavelengths from polychromatic UV light (MP) are absorbed by mono, di and tri chloramine. When these wavelengths are absorbed, the energy they carry breaks the chemical bond, effectively removing chloramines.

Operators also report improvements in water clarity and a reduction in TDS when using UV systems. Most are even able to turn the system off or reduce output overnight when the chloramine challenge is absent, and start the system in advance of opening the pool in the morning.

Ultimately, UV technology has an important role to play in the provision of safe, healthy water for recreational use.


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