Chlorination has been found to be very effective in killing bacteria which spread water borne diseases.
Small amounts of chlorine are added to your water to destroy any disease-causing bacteria. The amount of chlorine added is equivalent to less than half a tea cup in an average sized back yard swimming pool. This aims to ensure that all water is safe to drink right up to the time it reaches your tap.
It is important to maintain a minimal amount of chlorine throughout the entire system.
How is chlorine added and controlled?
By maintaining careful control and monitoring at each treatment plant and at specified points throughout the water supply system, chlorine levels can normally be maintained to levels below what is normally detected by customers.
However, changes in chlorine levels may occur if there are sudden increases in demands for water during periods of hot weather.
The chlorination process needs to meet water quality guidelines set by the 1987 guidelines set by the National Health and Medical Research Council and the Australian Water Resources Council.
Other methods of disinfection
Chlorination is the main method used to disinfect Melbourne's water supply. However, in some areas other methods of disinfection, namely chloramine and ultraviolet radiation, are used.
Chloramination is a modified form of chlorination where a small amount of ammonia is added to the water just prior to the chlorine addition to form chloramines which offer a relatively long lasting means of disinfecting water.
Why do we use chloramination ?
As well as providing a long lasting disinfectant, when properly used, chloramination will result in minimal taste and odour problems as compared to when chlorination is used.
What are the advantages of using chloramination?
- The disinfecting chemicals will last longer and therefore penetrate more effectively and further into the water supply system.
- Less likely to generate taste or odour problems.
- Chloramines are not broken down by sunlight to the same extent as when chlorine is used.
Chloramination is thus a very suitable treatment process for a water supply system where the treated water can be stored for an extended period of time as it requires significantly longer time to destroy any micro-organisms.
It can be used to advantage in closed systems where the water is held for long periods of time before consumption. It is most effective when the pH of the water ranges from seven to eight.
Where is it used?
Chloramination is already used successfully in parts of the Yarra Valley Water system, which supplies water from Monbulk to Mount Dandenong Ridge and from Silvan to Seville East. Some of the other areas throughout Victoria currently using chloramination include Geelong, Wodonga, and Bendigo.
The Ultra-Violet Light (UV) process uses ultraviolet rays to destroy micro-organisms in the water. Ultraviolet irradiation is at its best and most efficient in cold, very clear water which will reach the consumer quickly. It offers no protection against re-contamination.