Infections are caused by many pathogenic microorganisms simply known as germs. Disinfection is a process that kills germs, but not their spores, and reduces the risk of disease transmission. Public swimming pools and spa pool must maintain recommended disinfectant, pH and alkalinity levels to minimise the risk of disease transmission.

Last updated: 18 April 2013

Infections transmitted in swimming pools - minimising contamination

Infections are caused by the transmission of certain pathogenic micro-organisms known as germs. Transmission in swimming pools and spas occurs when germs are introduced into the swimming pool water, mainly by bathers, and then other bathers come into contact with them. There are many infections that may be transmitted by swimming pools and spas. The infections mainly infect the skin, ears, eyes, noses, lungs and the gastro intestinal tract. The infections can give rise to symptoms such as pussy sores on the skin, conjunctivitis in the eyes, runny noses, sore ears and burst ear drums, pneumonia, vomiting and diarrhoea.

The most serious risk to health is when there is a faecal accident in the pool. Faecal contamination is mainly caused by infants who are not toilet trained. Parents must take great care with their child's hygiene and ensure that they do not swim if they have had diarrhoea in the previous two weeks. Certainly, no person who has had diarrhoea is the previous two weeks should swim in a pool or spa.

It is important to minimise the entry of germs into a pool. Swimmers should always go to the toilet and shower before swimming. Cosmetics should be removed before swimming.

There are some situations which may allow germs to thrive. These include dirty pools, warm pools, aerated pools, pools with too little disinfectant, pools with too much stabiliser and chlorine disinfected pools where the pH is too high. A combination of these situations can easily lead to infection transmission.


Disinfection is a process which kills germs, but unfortunately not their spores. The aim of disinfection is to reduce the risk of transmission of infections. Disinfection is not an instantaneous process but takes time. The higher the concentration of disinfectant the more rapidly it kills. At the minimum recommended concentrations of chlorine and bromine, the kill time is about one minute or less for most germs.

Most germs are easily controlled by disinfection but Cryptosporidium oocysts and Giardia cysts, which are types of spores, are resistant to disinfectants. Their transmission needs to be controlled by preventing these germs and their spores from entering into pool or spa. There is a separate fact sheet about Cryptosporidium and Giardia.

Disinfectant levels above the recommended minimum concentrations must be present in the pool water at all times. Disinfection must be provided by a disinfectant which leaves an effective residual in the pool that is not harmful to swimmers.

Suitable disinfectants

Chlorine and bromine based disinfectants are the only satisfactory pool and spa disinfectants recognised by NSW Health for use in public swimming pools and spa pools. They also oxidise and destroy some organic chemicals which may enter the pool. These disinfectants provide a readily measurable residual in the pool water. Each disinfectant has its advantages and disadvantages and pool operators should consider any disinfectant or disinfectant system carefully before use.

Dosing of disinfectants

All public swimming pools and spas must, as a minimum, have continuous metered dosing equipment to continuously dose the disinfectant. Automatic dosing equipment should be used it is important to respond quickly to changes in chlorine demand in busy pools. Dosing systems must be active while the pool or spa is open and for at least one hour before and after the pool is open.

Efficient chlorine pools operate on the chemical process known as breakpoint chlorination which can only be reliably and constantly achieved with dosing equipment (see Continuous breakpoint chlorination).

Disinfection factors

  • Increasing pH decreases disinfection power so that above pH 7.6, chlorination is ineffective and above pH 8.0, bromination is less effective.
  • Stabiliser (cyanurate) should not exceed 50mg/L as disinfection becomes ineffective and chlorine levels should be increased if stabiliser is used. Stabiliser is not suitable for use with bromination.
  • Pools should be equipped with a circulation system and filters capable of producing clean, clear water. Filtered water is easier to disinfect, reduces contaminants and produces less by-products. Circulation systems should be operated at all times while the pool or spa is open, and for at least one hour before and after the pool is open.


Some of the chlorine and bromine is consumed in oxidising organic matter. This reduces the power and speed of chlorine and bromine to disinfect germs. This in turn could increase the risk of disease transmission. Oxidisers can often be used to oxidise or burn up organic matter and increase the disinfection power of chlorine and bromine, but their use should be specifically targeted perhaps once a week or fortnight and not used continuously. Oxidisers may affect the test results for chlorine and bromine.

Ultra violet light and ozone

UV light lamps and ozone systems may be used in addition to, but not instead of, chlorine and bromine to disinfect and oxidise swimming pool and spa pool water. UV light lamps must be located in the circulation system and not in the pool. Ozone must be dosed in the circulation system and quenched using activated carbon before the water returns to the pool. Low dose ozone systems, at less than less than 2 grams / hour generation, if installed correctly do not need ozone quenching.

Further information

The Public Swimming Pool and Spa Pool Advisory Document provides detailed explanations and information on disinfection, pool chemistry, risk assessment and other issues relevant to swimming pool operation.

Public swimming pool issues may be discussed with an environmental health officer at a local Public Health Unit: or at your local council.

In NSW call 1300 066 055 to talk to your local Public Health Unit.​

Current as at: Thursday 18 April 2013
Contact page owner: Environmental Health