Avoiding Recreational Water Illness Outbreaks

Recreational water illnesses (RWIs) are always a hot topic of discussion toward the end of summer when higher bather loads at aquatic facilities are faced with filters working overtime to keep pool water clean and clear. Unfortunately, there are always outbreaks—some bigger than others. The more severe the occurrence, the more likely it is to make mainstream media.

Cryptosporidium (Crypto) outbreaks happen every year. Unfortunately, traditional water sanitizers are not enough to battle this parasite, as it is highly resistant to chlorine and can linger in a pool for up to a week. When bather loads are high, and swimmers are swallowing water in the pool, facility managers need to have systems in place to help prevent the introduction of Cryptosporidium cysts, as well as systems to remove cysts from the water. That said, to avoid an outbreak, a two-pronged approach should be implemented:

  1. Taking physical steps to prevent the introduction of cysts into pool water by bathers.
  2. Employing secondary systems to: a) trap and remove Crypto cysts before swimmers ingest pool water; and b) deactivate the pathogen cysts so they are rendered inert and harmless should they be ingested.

Steps to Avoid an Outbreak

First, aquatic facility managers should put a prevention plan in place to try to avoid pool contamination. Should this fail, a secondary sanitation system should be used to remove dangerous Crypto spores from the pool, assuming they will likely enter the water at some point.

In the fight against 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 RWIs is still good old-fashioned chlorine. Due to its proven ability to disinfect, chlorine started to become popular for pool use in the '20s. Eighty years later, Life magazine called the use of chlorine as a disinfectant in water "one of the most important inventions of the last 1,000 years." When chlorine sanitizer is used against contaminants in pool water, there are varying contact time (CT) values that exist depending on the type of pathogenic (disease-causing) micro-organism.

For example, Giardia has a CT value of 45 minutes at 1 part per million (ppm) of chlorine. This means Giardia protozoa is inactivated in 45 minutes of contact with pool water carrying a 1 ppm residual of chlorine. To put things into perspective, Crypto has a CT value at 1 ppm of 15,300 minutes or 10.6 days. Therefore, it can remain active for a week, if not longer, in a standard chlorinated pool.

Recent studies conducted by the Environmental Protection Agency (EPA) have shown the average adult bather swallows up to 29.5 mL (1 oz) of water when swimming. Children typically ingest twice as much. 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 high bather loads.

Due to the fact Crypto is extremely chlorine-resistant and ranges between four and six microns, it is difficult to deal with. The majority of aquatic facilities still use sand filters, which are only capable of filtering down to 25 microns. Many residential pools, however, have filters that use diatomaceous earth (D.E.) media, which can pick up particles under four microns. This may appear to be the solution, and some service professionals may think Crypto would not be a problem in a pool with a D.E. filtration system; however, studies have shown Crypto cysts have the ability to elongate and press through filtration media in a viable state.

Current preventive measures for Crypto range from ensuring swimmers shower to keeping sick bathers out of the water. However, these measures alone are not enough to keep an outbreak from happening.

Other Methods for Dealing With RWIs

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

Ultraviolet light (UV) is another system that is quickly gaining in popularity. In fact, after an outbreak at a splash park in New York in 2005 the State of New York has mandated the use of UV on all public splash park facilities. However, high turbidity of the water can be a problem that could 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 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, and many private and publicly funded aquatic facilities do not have the budget to make these upgrades.

Some health departments also recommend hyper-chlorination methods when dealing with the suspicion of Crypto in pools. This typically entails raising chlorine levels between 20 and 30 ppm for eight to 12 hours. This method may vary depending on local health regulations. In 2004, however, the CDC reported there was no conclusive evidence to prove complete eradication of Crypto using this recommended method.

In North America, the standard protocol for water quality maintenance (WQM) is premised on the assumption that appropriate filtration and residual halogen disinfection will inactivate all pathogens. Experts agree that moving beyond the basics will require revising the two-pillar approach that includes filtration and halogen, and adopting supplemental disinfection for water quality management in pools and spas.

The costs involved in preventing RWIs using ozone, UV and regenerative filters can create sticker shock for those aquatic facility managers who have budget constraints. As a result, it may prevent some smaller facilities from taking these additional measures.

Inline UV disinfection is recognized as an extremely effective and reliable method for deactivating pathogens in the water and reducing the bather's exposure to disinfection byproducts. Some public health authorities are already beginning to mandate supplemental inline UV disinfection. After the Crypto outbreaks in upstate New York, New York State now mandates supplemental inline UV disinfection on all public splash parks as do several other states and provinces, such as Florida, Ontario and others.

Regular dilution of water is another means of reducing the risk of RWIs. This is already practiced by public pool facilities in Europe where there are requirements for an entire pool being diluted with fresh water over a month's time. Some other standards suggest adding 30 L (8 gal) of fresh water per day for every bather in the pool. This is obviously not viable in most areas of North America, especially those where regular droughts occur throughout the summer months.

In some areas, chemically laden pool water cannot be put to waste as it goes directly through the aquifers and could contaminate the groundwater. UV-treated water usually has drastically reduced sanitizer levels and, as a result, can safely be drained.

Enhanced Filtration

One viable and more affordable method that any aquatic facility can begin using immediately is enhanced filtration. The CDC and many aquatic experts have long considered filter enhancement with the use of specialty clarifiers as another preventive method. This technology uses two opposing biopolymers that quickly and effectively entrap micro-organisms such as E. coli and Crypto.

This method has been proven through an independent study conducted at Auburn University, which was presented at the World Aquatic Health Conference (WAHC) in 2005. The study showed very stable flocs of Crypto were able to form and be held in simulated sand filters. According to a presentation on "Cryptosporidium Removal from Swimming Pools by Sand Filters" by James Amburgey, Ph.D., an associate professor at the University of North Carolina at Charlotte, at the 2006 WAHC, there was a 99.99 percent removal of Crypto from pool water using sand filtration treated with the two-stage polymer.

There is a great deal of complicated physics going on in a depth filter, such as the sand bed, as it traps particulates suspended in the incoming water. Other influences include surface charge, particle size, conformation, rigidity, density and so on, on the nature of the path taken by the particles, and the frequency of their collisions and interactions with the filter medium. However, it is simple enough to understand the overall outcome: Smaller particles tend to make it through the bed and come out in the effluent, whereas the larger particles stand a greater chance of becoming stuck and trapped along the route.

Of course, all those retained particles alter the total amount of path available within the filter bed for the next influx of water. On the other hand, the filters should be periodically backwashed, which will restore the pathway for future entrapment. In this way, properly maintained depth filters do a fine job of keeping pool water free of much of the undesirable bits and pieces that become suspended in the media during normal use.

Giving pool filters the ability to trap more is the idea behind enhanced filtration products.

Enabling filter media to remove particles that were in the submicron range allows for the removal of microbial organisms. The most troublesome of those measure only a few microns or even less, and therefore routinely pass through filters with the flow of water.

Molecular weight, shape and charge, as well as absolute and relative concentrations of the biopolymers, plus timing of exposure, all turned out to be critical factors. Data from laboratory experiments conducted at Auburn University showed with the proper polymer treatment, inert particles (in this case, bentonite clay) could be flocculated into larger clumps, enabling many of the resulting aggregates to be removed in a single filter bed pass. Later experiments involving biological, as well as other inert particle types showed similar success, even to the extent suspensions of live Crypto cysts could be removed at a rate of 99.9 percent in a single pass through sand.

Accomplishing this required sequential treatment of pool water with two differently acting biopolymers—one charged positively, the other negatively. Using the right proportions and concentrations, this could be achieved reliably and repeatedly.

Here Is How It Works


Polymer molecules from stage one alter surface charges on small particles in the water, destabilizing the normal tendency they have to repel one another (and therefore keep separate, and fully suspended, indefinitely). The particles aggregate and become enmeshed in the lattice of long, cross-linked polymer molecules to form much bigger clumps. If the concentration of the cationic (positively charged) polymer is too low or high, this will not occur. Stage two polymers (negatively charged) then entangle the complexes, firming them up so they can withstand being trapped in the filter bed, until the filter is backwashed, removing them to waste.

The net effect is Crypto cysts, normally able to pass through sand bed and other particulate filter media, become trapped as cyst-polymer complexes and are removed. Crypto is not the only biological agent that can be trapped in this manner; other waterborne microbes (e.g. Giardia, E. coli) are similarly affected.

Stage one and two polymers can be used while bathers are present. With particle removal possible at the submicron level, overall water clarity also improves. This gives sand filters the ability to trap minute particles, and offers aquatic facility managers a new way to fight RWIs while improving water clarity.

Polymer additions for large pools can be accomplished by controlled metering, but a properly timed manual process is also entirely practical for smaller scale operations.

A Real-Life Example

Elise Knox, an aquatic facility operator in the Dallas/Fort Worth, Texas, region, along with a staffer, attended a CDC state aquatics seminar in an effort to be prepared with a plan to avoid a Crypto outbreak, and that she did when her area was hit hard with an outbreak in 2007.

"We knew we couldn't budget for UV filters in all of our pools, but we needed to prepare because an area-wide outbreak would be sure to affect us," Knox said. "In this case, we decided to use the enhanced filtration method. We were the first pool in the area to use it, in fact.

"We have used this method now for more than seven summers, and we've had the side benefit of excellent water clarity."

According to Knox, when the outbreak occurred, they hyper-chlorinated the pool water as per CDC recommendations. "Chlorine is not the be-all-and-end-all solution; it's a clean-right-now solution only," said Knox. "I like to compare hyper-chlorinating to washing a doorknob during flu season. The next person that comes along and sneezes on your doorknob, it's back to the same mess."

This facility's Crypto prevention plan also included methods to help keep it from entering pool water with the following: On weekdays, when children are most likely to come to the pool alone, a mandated restroom/hydration break at 3 and 5 p.m., was established. Every child age 7 through 17 is required to exit the pool for 30 minutes and are encouraged to stop at the water fountain for a drink and strongly encouraged to use the restroom (so they do not go in the pool). The facility also established a website for patrons to read about its prevention methods, as well as provide informative links on CDC's website.

"We've always concentrated on 'low tech' methods, but this really showed our staff why we actively work to enforce the 'shower before swimming' and 'no spitting or spouting' rules," Knox said. "We also displayed clever signs and funny posters the CDC has on their website for our facilities, reinforcing these same rules.

"In the end, our patrons actually thanked us for enforcing the rules. It was amazing how supportive our patrons became as we explained why we had breaks and required showers."

A Continuing Challenge

RWIs, especially Crypto, continue to be a major challenge for pool professionals. New water treatment technology and multiple water maintenance procedures are key to maintaining healthy water in aquatic facilities. These layers will include a residual of chlorine sanitizer, ozone or UV, regular dilution of pool water, and enhanced filtration of micro-organisms using the recommended polymer system.



Terry Arko has more than 30 years of experience in the pool and spa/hot tub industry, working in service, repair, retail sales, chemical manufacturing, customer service, sales, and product development. A certified pool operator (CPO) and CPO instructor through the National Swimming Pool Foundation (NSPF), Arko is currently a water specialist for NC Brands, parent company of SeaKlear and Natural Chemistry, which is a manufacturer of pool and spa products. For more information, visit www.ncbrands.com.