The continual addition of residual disinfectant to a public swimming pool or spa pool is essential to adequately disinfect the pool and minimise the health risk at all times.

Last updated: 18 April 2013

Legislation

Clause 3(1) of Schedule 1, Public Health Regulation 2012, requires that a public swimming pool and spa pool must be fitted with an automated or a continuous metered disinfectant dosing system.
 
It is dangerous to hand dose a public swimming pool or spa pool while the pool is open to swimmers. Yet, disinfectant must be continuously added to achieve adequate minimum disinfectant levels and this must be done through an automatic or continuously metered disinfectant dosing system.
 

Continuous metered disinfectant dosing system

A "continuous metered disinfectant dosing system" is a device or apparatus which delivers the disinfectant in a controlled continuous and steady rate. The disinfectant must be delivered at some point into the pool circulation system and not directly into the pool. It is preferable that the disinfectant be added just after the filtration system to lessen the formation of disinfection by-products.
 
A pump which delivers liquid chlorine at a particular rate i.e. millilitres per hour, is a good example of a continuous metered disinfectant dosing system. Other examples include dry chemical feeders, and electrolytic disinfectant generation.
 
Obviously hand dosing or broadcasting is not a continuous metered disinfectant dosing system. Similarly a floating device with a block of disinfectant is not a continuous metered disinfectant dosing system. An erosion feeder is not a continuous metered disinfectant dosing system unless it can deliver the disinfectant at a constant continuous rate instead of at a diminishing rate.
 
One of the cheapest forms of a continuous metered disinfectant dosing system is a peristaltic pump. These draw liquid chlorine (sodium hypochlorite) preferably from a shaded drum and slowly inject the liquid chlorine into the pool circulation system after the filter. The peristaltic pump can be set up to deliver a dose of chlorine at particular time intervals. A continuous metered disinfectant dosing system can also be controlled by a timing switch to activate it at some time prior to opening and de-activate it at some time after closing. The dosing rate or frequency on some pumps can be varied allowing the pool operator greater scope in delivering disinfectant to the pool at varying continuous rates.
 

Automatic dosing system

An automatic dosing system uses probes to detect disinfectant levels or activity. This information is fed back to a controller which automatically adjusts the dose rate of the continuous metered dosing system. There are various levels of sophistication with automatic dosing systems which may include data logging, and download capabilities.
 

Further information

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. It may be found at the NSW Health swimming pool web site at:
 
Public swimming pool issues may be discussed with an environmental health officer at a local Public Health Unit: http, or at your local council.
 
In NSW call 1300 066 055 to talk to your local Public Health Unit.
Page Updated: Thursday 18 April 2013