A recent article published by The Washington Post discusses an outbreak of the bacterial infection known as Legionnaires’ disease which reportedly affected eight Milwaukee area people in 2010. The outbreak has been linked to a decorative water feature located in a hospital lobby that had been visited by all eight of the people who contracted the illness. This and other similarly documented cases have raised question as to the risk factors associated with operation of such water features in public spaces, particularly those frequented by persons who may be immunodeficient, such as health care facilities.
Legionnaires’ disease is a fairly common topic in the commercial aquatics industry, as this condition is caused by a waterborne pathogen known as legionella bacteria. The illness is a dangerous form of pneumonia and is contracted by inhaling aerosolized water droplets that contain the legionella bacteria. Infections have, in the past, been linked to poorly maintained spas or hot tubs (both commercial and residential) as well as other types of public bathing places.
Legionella bacteria is naturally occurring and is commonly found in many water sources, including municipal drinking water, but typically at a concentration below that which would cause infection. However, if there is a source of the bacteria, and conditions are favorable, the bacteria can quickly multiply to levels that may pose a health risk. For this reason, it is critical that any water feature, especially those which create aerosolized water, is treated and maintained in such a way to control the presence of legionella bacteria along with other waterborne pathogens.
Most people, whether aquatic professionals or not, understand the purpose of treating and balancing swimming pool water to maintain a safe environment for swimmers. Unfortunately, the importance of this protocol is sometimes overlooked in water features such as fountains that are not meant for direct interaction, but nevertheless can expose people to waterborne bacteria. The health risk is by no means limited to aquatic facilities and water features. Legionellosis outbreaks have been linked to many other types of water systems, including irrigation, car washes, water softeners, cooling towers, and even showers. An ASHRAE standard exists for the purpose minimizing Legionellosis risk associated with building water system design and operation.
As for the case described in the previously mentioned article, the culprit was found to be a “water wall” style feature located in a main lobby area of a hospital. The affected individuals had been exposed to legionella as they sat next to or passed by the feature and presumably inhaled aerosolized water droplets emitted by the cascading effects of the water wall. This case took place in a hospital, but just as easily could have been a restaurant, or bank, or any other public space with an inadequately maintained water feature. The point here is that regardless of the water feature type or setting, a method of disinfecting the water and maintaining the feature must be employed to prevent the growth of bacteria and ensure the feature is safe.
There are various options for disinfection of aesthetic water features. Many of the same technologies that are used to disinfect swimming pool water are applicable to aesthetic water features as well. These include a halogen residual (chlorine or bromine), ultra-violet light, ozone, and copper-silver ionization. Selection and design of an appropriate system is typically dictated by the size and type of the feature, including the volume of water it will contain, as well as the setting in which it will operate. Filtration is also important, particularly in larger scale water features, to prevent build-up of particulate and contaminants that can contribute to bacteria growth.
Beyond the disinfection systems, design of the feature itself also plays a key role in maintaining a healthy water feature. Stagnant water areas must be avoided by providing adequate circulation throughout the feature – not only for the main body of the feature, but any concealed volume or reservoir as well. Feature flow types should be considered for the setting in which the feature will be located, minimizing the aerosolizing of water when necessary. Material selections must be appropriate, avoiding porous materials that can harbor bacteria growth. The second outbreak case referenced in the Washington Post article mentioned previously describes a “spongelike foam material” used as a base for a bed of decorative rocks that the water feature flowed through. A porous material such as this foam provides extensive surface area and interstitial space in which bacteria can readily reproduce without being exposed to good water circulation and thus disinfection. Even when draining down a feature of this type for cleaning, it would be nearly impossible to adequately clean this type of material by any measure short of replacing it. It is for these same reasons that porous materials should be avoided on swimming pool decks and spray pad surfaces as well.
Observable water features have been popularized in many environments - both indoor and out - for the unique aesthetic, soothing ambiance, and therapeutic presence that can be created by moving water. These benefits, however, do not come without risk if the prevalence of waterborne pathogens is not properly addressed. Ultimately, the design of and aesthetic water feature, regardless of type or setting, should be undertaken with the assumption that human interaction will take place - even if it is simply a passer-by taking a breath. Any feature that maintains a volume of water must also treat that water in order to ensure it is sanitary. These systems may be very simple, or may consist of multiple, fully automated sanitizing and monitoring components on par with the largest commercial swimming pool systems. In addition, a testing protocol should be established for the water feature to monitor the water quality, ensure the equipment is operating properly, and the systems are maintained appropriately. If these criteria are addressed when considering installation of a water feature, it can provide years of safe and sanitary operation. Such a feature should be able to be enjoyed in a hospital lobby, without prompting a return trip to the hospital due to Legionnaires’ disease.