How the Waikato River water is treated
Step 1: Coagulation and clarification
After first passing through a screening filter to remove large debris such as leaves and branches, coagulant (aluminium sulphate or ‘alum’), lime, and carbon dioxide are mixed into the water. This causes the tiny dirt particles to stick together, making for easier removal. The water is then piped into settling tanks, where the mixture of alum and dirt (known as ‘floc’) sinks to the bottom of the tank.
Step 2: Membrane filtration
The clarified water is then treated by advanced, ultra-filtration membrane technology to remove pathogenic organisms. The pores of the membrane filters are so small (about 15 times smaller than the filter system in household water filters) that they prevent the spores of parasites, giardia, and cryptosporidium from passing through.
Step 3: Granular activated carbon filtration
During this stage, any organic compounds are adsorbed onto carbon particles. Carbon also removes any unpleasant tastes or odours from the water.
Step 4: Chlorine treatment
In the final stage, chlorine is added to the water to kill any remaining viruses and prevent bacterial growth during storage and transportation. The sophistication of the treatment process means the Waikato Water Treatment Plant uses around one-third less chlorine than Watercare’s other treatment plants.