Water goes through several stages of purification. Each stage helps to ensure water is clean and free of potentially harmful bacteria and other microorganisms. Water treatment generally involves the following steps:
- Raw water settling: river water is collected in a reservoir or basin where debris and large particles can settle out through gravity.
- Coagulation: as the partly settled water enters the treatment plant from the reservoir, chemical agents are added. These agents allow dissolved substances and small particles (including microorganisms) to coagulate (join together) into tiny clumps.
- Flocculation: with further gentle mixing, the tiny clumps of joined material form larger, visible masses known as ‘floc’.
- Clarification: water can now be clarified (made clear) by removing it from the solid floc material. This can be done either by settling of the floc using gravity, or by flotation of the floc using air bubbles.
- Filtration: the clarified water is passed through large filters made from layers of sand and other granular materials to remove any remaining floc. Once through the filters, water appears clear and clean.
- Disinfection: Some bacteria and viruses may remain in the filtered water, and for this reason small doses of disinfecting agents are added. Chlorine and chloramine (a combination of chlorine and ammonia) are the most commonly used agents and are essential for ensuring customers are never at risk of water-borne illness from drinking tap water. Very low levels of chlorine or chloramine are maintained in the distribution system (sometimes by use of a booster dosing unit) to protect the safety and quality of water in storage tanks and pipes. As part of a multi-barrier approach, ultraviolet light may also be used to provide an additional level of disinfection for some systems.
1) A ‘Jar Test’ is undertaken in the lab to calculate what chemical amounts are required
2) Water is observed under a microscope
3) View from on top of the clarifier tank at Toora Water Treatment Plant
4) View over the top of the treated water storage tank at Toora Water Treatment Plant