Monitoring and Management > 5. Water >
Describe and assess the effectiveness of methods used to purify and sanitise mass water supplies
- The steps involved in the purification and sanitising of water supplies are:
- Screening: The removal of large debris.
- Aeration: The increasing of dissolved oxygen by spraying, which causes iron salts to be oxidised to insoluble oxides.
- Flocculation: The coagulation of colloidal and particulate matter to form flocs.
- Sedimentation: The settling of flocs to form a sludge.
- Filtration: Formation of clear water by removal of substances that cause turbidity and colouration, using beds of sand and gravel as well as charcoal filters.
- Chlorination: The disinfecting of water using chlorine gas and various hypochlorites, which kill microorganisms.
- pH Adjustment: The adjustment of pH to between 7 and 8.5 using buffering chemicals.
- Fluoridation: Adding of fluoride compounds to help prevent tooth decay (resulting in a fluoride concentration of about 1 ppm).
- The treatment of mass water supplies requires a balance between cost, speed and the quality of the finished product.
- Current methods are not perfect at removing disease-causing agents, as shown through events such as the Giardia and Cryptosporidium incident in Sydney in 1998.
- Further techniques could be introduced, such as the use of membrane filters and ozone sterilisation, although this would be much more costly.
- Instead, water is monitored daily at treatment plants.