The water is first filtered using a simple screen. This retains the largest pieces of waste found in the water (leaves, insects, particles larger than 1 mm).
It then passes through fine metal meshes which retain the smaller pieces of waste.

A coagulating product is added to the water thereby bringing together into flocs any waste still present in the water (dust, soil particles, fish eggs etc).
As these flocs are heavier than the water, they settle at the bottom of the sedimentation tank. 90 % of suspended matter is removed as a result of this.

The water passes through a filter, either a fine sand filter bed and/or an activated carbon filter.

Sand filtration removes matter still visible to the naked eye.
Activated carbon filters retain micro-pollutants such as pesticides, and consume some of the organic matter "broken down" by the ozone.
There are other even more robust filtration processes such as membrane filtration.

Ozone is used to disinfect water, as it destroys bacteria and viruses.
When mixed with water, this gas also has an effect on organic matter by breaking it down into pieces. It also improves the colour and taste of the water.

Ozone is a slightly bluish gas. This is due to the transformation of the oxygen content in the air as a result of electrical discharges (or ultra-violet rays). It is produced in ozonators.

Chlorine is added to the water when it leaves the water treatment plant and at various stages throughout the distribution system. This is to prevent bacteria from developing and to maintain water quality throughout the entire water mains system.