Water needs to be treated to make it safe to consume. The types of treatment depend on where the water comes from (e.g. dam, bore or river), environmental conditions and what activities happen in and around the water.
Water treatment plants have a range of processes to suit the water supply source and may include one or more of these processes.
Water from rivers, creeks and dams contains debris like sticks and leaves that can block water mains and pumps, and cause problems during treatment. These larger objects are removed as the water passes through a coarse stainless steel screen.
Soda ash (sodium carbonate) is added to the water to raise the pH of the water.
Water often contains suspended particles of clay and other matter that need to be removed. These particles have a negative charge and repel each, which means they stay suspended in the water. When a coagulant is added to the water, the charges of the particles are neutralised, and they clump together forming heavier particles that settle out of the water. Coagulation also helps with pathogen removal and is a key component of conventional water treatment. We use alum-based coagulants.
Filtration removes heavy, settled solids after chemical mixing and involves a media like sand and carbon. Carbon absorbs odour, taste and discolouration.
- Malanda, Millaa Millaa and Yungaburra have multi-media filtration that uses layered gravel, sand, anthracite and activated carbon.
- Davies Road has four, deep-bed media filters each containing two media layers. The bottom layer is crushed basalt and the top layer is quartz sand.
- Herberton has eight, dual-bed media filters that use garnet, filter sand and anthracite.
Ultraviolet (UV) light is generated by low and medium pressure mercury vapour lamps and is an important part of the multi-barrier water treatment processes. Ultraviolet light is passed through the water and inactivates viruses, bacteria and protozoa. UV is particularly effective in destroying Cryptosporidium, which is resistant to chlorine. UV has minimal effect on the chemical composition or taste of the water.
The final step for water treatment is chlorination. Chlorine is added to the water to disinfect any remaining microorganisms. Some chlorine remains in the water to continue treatment and protect the quality as it travels to properties.
We monitor chlorine (and other parameters) several times a week from multiple locations and periodically send samples for testing at a National Association of Testing Authorities laboratory. The level of chlorine changes depending on conditions but we ensure the levels remain within the Australian Drinking Water Guidelines. Chlorine has an odour threshold in drinking water of about 0.6 mg/L, but some people are particularly sensitive and can detect amounts as low as 0.2 mg/L. We may need to exceed the odour threshold to maintain effective disinfection. This is why you can sometimes smell the chlorine in your water.