Layer Technology

Recreational Water Illness (RWI) has been a hot topic this past year. In fighting these stealthy germs, industry professionals use several approaches based on research, health department regulations and current Centers for Disease Control (CDC) recommendations.

One of the most effective tools to prevent the threat of swimmer sickness is still the old-fashioned chlorine sanitizer. In fact, chlorine has a long history of effectively destroying water invaders. In London during the 1800s, more than 25,000 people died in less than a decade due to cholera from raw sewage in the River Thames. In 1855, London became the first city to treat sewage with chlorine. As a result, cholera cases were reduced to nearly zero. The use of chlorine for drinking water in the United States reduced cholera cases from 25,000 in 1900 to only 20 in 1960.

Because of its proven ability to disinfect, chlorine became popular for swimming pool use in the 1920s. In 2000, Life magazine called the use of chlorine as a disinfectant in water “one of the most important inventions of the last thousand years.”

Do The Math

When chlorine sanitizer is used against contaminants in pool water, varying contact time (CT) values exist, depending on the type of pathogenic (disease-causing) microorganism.

For example, Giardia has a CT value of 45 minutes at 1 ppm of chlorine. That is, a Giardia protozoa is inactivated in 45 minutes of contact with pool water carrying a 1-ppm residual of chlorine.

The problem child of pathogenic microorganisms is Cryptosporidium (Crypto)--which has a CT value of 9,600 minutes or 6.7 days--so it remains active for a week or longer in chlorinated pools. Recent studies conducted by the EPA have shown that the average adult swimmer swallows up to one ounce of water while swimming, and children usually swallow twice as much as adults. With the possibility of billions of chlorine-resistant Crypto cysts present in pool water, it is easy to see how swimmers can become infected. This is especially true in pools with a high bather load.

Crypto is extremely chlorine-resistant, and has a size of 4 to 6 micron, making it difficult to control. The majority of public facilities still use sand filters that only filter down to 25 micron. Many residential pools use diatomaceous earth (DE) filters that can pick up under 4 micron. While the DE filter may appear to be a solution to the problem, studies have shown that the Crypto cysts actually have the ability to elongate and press through filtration media in a viable state.

Existing preventative measures for Crypto hardly seem effective, currently ranging from ensuring swimmers shower to keeping sick swimmers out of the water.

Hyperchlorination methods are recommended by health departments to deal with the suspicion of possible Crypto in pools. The hyperchlorination method is typically 20 to 30 ppm for eight to 12 hours. This method may vary depending on local health regulations. CDC reported in 2004 that there was not conclusive evidence to prove complete eradication of Crypto using this recommended method.

New Methods To Deal With RWIs

Ozone is becoming popular as a possible backup means for eradicating Crypto. Ozone kills bacteria and Crypto cysts 3,125 times faster than chlorine.

Ultraviolet light (UV) is another system quickly gaining popularity. After an outbreak at a splash park in New York last summer, the state mandated the use of UV at all public splash park facilities. High turbidity of the water can be a problem that may cause UV systems to become ineffective against Crypto. For this reason health departments also regulate turbidity levels in public pools.

The biggest problem with many public facilities is that they rely only on chlorine, and use sand filtration. Thus, to effectively deal with Crypto, expensive upgrades--such as ozonators and UV units--need to be installed. Many private and publicly funded aquatic facilities simply don’t have the budget to make such vast improvements.

Regular dilution of water is another means of reducing illness risk. This is already practiced on public pools in Europe, where the entire pool must be diluted with fresh water over a month’s time. Some other standards suggest adding 30 liters a day of fresh water for every swimmer in the pool.

Enhanced Filtration

Another viable method that any facility or pool can begin using immediately is enhanced filtration. The CDC and many aquatic experts have long considered filter enhancement with the use of specialty clarifiers. This technology uses two opposing biopolymers that quickly and effectively entrap microorganisms, such as algae, E.coli and Crypto. This method has been soundly proven through an independent study conducted at Auburn University. The study showed stable flocs of Crypto were able to form and be held in simulated sand filters. There was a 99.99 percent removal of Crypto from pool water using sand filtration treated with the two-stage polymer.

Although RWIs--especially Crypto--continue to be a major challenge for pool professionals, multiple technology layers will most likely be the key to providing safe and disease-free swimming pools.

Terry Arko has worked in the pool and spa industry for over 25 years, and has experience in service, equipment repair, retail management and chemical manufacturing. A Certified Pool/Spa Operator, he has spent the last 14 years as a technical consultant specialist in chemical water treatment. Terry is a Products Specialist for SeaKlear Pool and Spa Products, located in Bothell, Wash.