LEGIONELLA - World Health Organization

Various additives may also be used to help maintain the water balance; for example, cyanuric
acid helps to stabilize chlorine, particularly in outdoor pools, by preventing its breakdown by
UV light and sunlight. Bicarbonates or carbonates may be added to act as a buffer against
rapid changes in pH caused by high bather loads, pollutants and chemicals.
In some circumstances, such as in natural spring-fed spas, the addition of chemical disinfectants
is considered an adulteration and is not usually allowed, because of the reputed therapeutic
effects of the natural water (Martinelli et al., 2001). Since disinfectants are not used, options
for control strategies are limited. Pasteurization is the most common means of control, combined
with flushing of outlets for 5–10 minutes. The interval between flushes must be based on a
risk assessment of the particular system.
Similarly, if mineral water at a hydrotherapy facility is inhaled for its claimed beneficial or
therapeutic effects, disinfection might not be considered acceptable, because it would change
the chemistry of the water. However, UV treatment may be acceptable, provided the water is
not turbid. UV combined with filtration could be used if there is high turbidity.
Design, operation and maintenance — control measures
Systems should be designed, operated and maintained to optimize control strategies. For
example, decreasing the available surface area within the system and associated pipework will
reduce the potential for bacterial colonization, and avoiding the use of non-metallic materials
in construction will help to reduce the risk of Legionella growth.
Types and design of materials
Only materials that have been tested and shown to be suitable for use in contact with potable
water should be used in the construction and installation of pool, hot tub or spa systems. In
choosing materials, their potential to resist microbial growth should be taken into account;
this includes not only the surfaces of the pool, but also the materials used for pipes and seals.
Materials used during installation, such as jointing compounds, sealants and washers, should also
be considered for their potential to support microbial growth. It is not advisable to use items made
from natural materials, such as hemp and natural rubber, because these components promote biofilm
formation, as discussed in Section 4.3.2 of Chapter 4 (Niedeveld, Pet & Meenhorst, 1986).
Pipework in hot tubs should have a minimal surface area, which should be smooth so that it
does not support colonization by biofilm bacteria. Flexible, corrugated pipework should be
avoided, because this increases the surface area and may allow water to be retained in valleys,
both of which increase the risk of colonization.
Pipework should also be easily detachable for draining and cleaning — even small volumes of
stagnant water will pose a threat from microbial growth in biofilms. There should be adequate
access to all parts of the system, including the balance tank and associated pipework. The air
and water jets should be removable for physical cleaning and disinfection.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS