Water treatment processes

During coagulation, liquid aluminium sulfate (alum) and/or polymer is added to untreated water (raw water). When mixed with the water, this causes the tiny particles of dirt present to stick together or coagulate. These groups of dirt particles then join to form larger, heavier particles called flocs, which are easier to remove by settling or filtration.

As the water and the floc particles progress through the treatment process, they move into sedimentation tanks. Here, the water moves slowly, causing the heavy floc particles to settle to the bottom. The floc that collects at the bottom of the tank is called sludge, and is piped to drying lagoons. In direct filtration, the sedimentation step is not included, and the floc is removed by filtration only.

Water flows through a filter designed to remove particles from within it. The filters are made of layers of sand and gravel, and in some cases, crushed anthracite. Filtration collects the suspended impurities in water, enhancing the effectiveness of disinfection. These filters are routinely cleaned by backwashing.

Water is disinfected before it enters the distribution system to ensure that any disease-causing microorganisms are destroyed. Chlorine is used because it is a very effective disinfectant, and residual concentrations can be maintained to guard against possible microbial contamination in the water distribution system.

Solids that are collected and settled out of the water by sedimentation and filtration are removed to drying lagoons.

Water fluoridation is where community water supplies are treated with a concentration of the free fluoride ion. This is adjusted to an optimum level to reduce dental decay. We're required to fluoridate in accordance with the NSW Fluoridation of Public Water Supplies Act 1957.

Lime is added to filtered water to adjust the pH and stabilise the naturally soft water. This minimises corrosion in the distribution system, and within customers’ plumbing.