There is a 5 stage process to this type of purification:

1. Microfiltration - Water from the tap is fed under pressure to a very fine filter which stops any sediment or debris going any further.

2. Granular Activated Carbon filter - this filter is most effective at removing chlorine and volatile organic compounds (VOCs) from the water. Carbon filtering is a method of filtering that uses pieces of activated carbon to remove contaminants and impurities, utilizing chemical absorption from the water.

3. Block Activated Carbon filter - It is the same as above but it is a block of activated carbon thus giving it a finer filter and more thorough. 

4. RO membranes - Reverse Osmosis membranes is a filtration method which removes large molecules and ions from the water by applying pressure to the water as it travels through, allowing only water molecules to pass. The membranes used for RO have a dense layer of polymer matrix where the separation occurs allowing water through but preventing the passage of solutes such as salt ions.

5.Resin Filter - Also known as De-Ionising vessel. This final process in effect polishes the water. When the water leaves the RO stage it is about 95% pure, however when it passes through the DI vessel which is a mixed bed of anion and cation resins the water then leaves the process 100% pure.