How is it Treated?

The Waikato Treatment Plant uses world leading technology, which has already proved effective in other treatment plants around the world.

The four-stage, ultra-filtration treatment process

1. Coagulation and clarification - Here coagulant (aluminium sulphate), lime and carbon dioxide (to adjust the pH) are added to the raw water. The coagulant causes particles in the water to clump together into larger particles called floc which are easier to remove during clarification. The coagulated water is then passed through clarifiers. The coagulated solids settle at the bottom of the clarifiers while the clarified water is decanted from the top. The coagulated water is then fed through settling plates and a blanket of sludge solids. The floc clings to the sludge which is then removed.

2. Membrane filtration - The water is then treated by advanced, ultra-filtration membrane technology which is considered by international experts to be a fully effective barrier to pathogenic organisms in water and guarantees against contamination from parasites such as giardia, cryptosporidium and most viruses.

3. Granular activated carbon filtration - Here any organic compounds are then absorbed into the carbon particles where they remain or may be broken down by the action of harmless bacteria. The carbon also removes any unpleasant tastes or odours from the water.

4. Chlorine treatment - The water is finally treated in a chlorine tank to kill any remaining viruses and prevent bacteria growth during the water's storage and transportation. About 30-40 percent less chlorine will be needed than at Watercare's other treatment plants because the water will be of a much higher standard.

Membrane filtration technology is used successfully in other developed countries including France, America, Canada and Great Britain. In most cases, the raw water being treated in those overseas plants contains far more pollutants, bacteria and viruses than the Waikato River.

Ontario, Canada, has used the technology for the past three years. The Ontario Public Utilities Commission says the membrane technology has proved an "absolute barrier" to harmful contaminants, and that due to the success of its operation, 12 similar plants have been constructed around Canada.