LEGIONELLA - World Health Organization

forms are available (e.g. gaseous, granular, liquid, tablet), with varying amounts of available
(free) chlorine, so it is important to follow the manufacturer’s instructions carefully. Sufficient
disinfectant should be added so that there is still free, active biocide after combination with
bacteria, urine and other organic pollutants. The free chlorine residual recommended by the
WHO for hot tub water is at least 1 mg/l (WHO, 2006); in the USA, it is 2–5 mg/l (CDC,
2005) 10 ; in South Australia, it is 2–4 mg/l (Broadbent, 1996) 11 ; in the UK it is 3–5 mg/l
(HPA, 2006).
When chlorine is in water it combines with organic materials arising from the bathers, such
as urine and perspiration, to form chloramines. These act much more slowly than when chlorine
is free or uncombined; they also give rise to odours. Ideally, the level of combined chlorine is
nil, but up to a value equivalent of one-third of the total chlorine is acceptable (HPA, 2006).
Bromine-based products such as bromochlorodimethylhydantoin (BCDMH) are often used
in hot tubs. When BCDMH dissolves in water, it produces a solution of hypobromous and
hypochlorous acid. Bromamines are formed from bromine-based disinfectants in a similar
way to chloramines; however, bromamines are still effective as a biocide and are less susceptible
to changes in pH. In bromine-treated pools, a residual of 4–6 mg/l of total bromine is
recommended.
Ozone is often used in combination with chlorine or bromine; it can be very effective, but it
is not suitable for use on its own. Excess ozone is removed by the use of a charcoal filter.
Practical aspects
Features such as water sprays in pool facilities should be periodically cleaned and flushed with
a level of disinfectant high enough to eliminate Legionella species (e.g. at least 5 mg of free chlorine
per litre) (WHO, 2006).
In hot tubs in commercial premises, the introduction of water treatment chemicals should be
automatically controlled. Intermittent dosing by hand will not achieve a consistent level of
biocide and is not recommended.
The pH value indicates whether the water is acid or alkaline. Maintaining a pH range of
7.2–7.8 for chlorine and 7.2–8.0 for bromine-based and other non-chlorine processes is
important for bather comfort, for safety (by controlling disinfectant activity), and for control
of corrosion or chemical attack within the pool system. In unusual situations where there is
a maintenance fault, the pH could drop to levels at which oxidizing biocides will be disassociated,
leading to increased levels of chlorine or bromine, which can cause eye and skin irritation. At
high pH levels, the chlorine will remain bound and be less effective.
10 http://www.cdc.gov/healthyswimming/pdf/spa_operation.pdf (accessed 29 March 2006)
11 http://www.dh.sa.gov.au/pehs/publications/monograph-heated-spas.pdf (accessed 29 March 2006)
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS