Other filter options

If you want to buy a filter to remove any chemical contaminants, look for one which complies with NSF standard 53 (Health Effects) or the Australia/New Zealand water filter standards AS/NZS 4348 or AS 3497:1998. The label should list clearly what it will remove.

Filters can be mixed and matched to increase the number of contaminants removed. Activated carbon may be combined with an ion exchange unit to remove some metals and improve taste. Pre-filters are often used to remove sediment so that the filter works better and doesn't clog quickly.

Ion exchange

These filters contain resins which attract either positively charged or negatively charged chemicals. Most models contain a mixture of both types.

Depending on the resins, they can remove positively charged chemicals such as metals or negatively charged metals such as fluoride or nitrate. They will also soften hard water.

On their own they won't remove chlorine or pesticides, and they don't work well when the water contains a lot of sediment, for example in an unfiltered supply. The cartridges require frequent changing.

Reverse osmosis

These filters remove most contaminants. Water is passed under high pressure through a thin membrane. Most contaminants are physically blocked and washed away. Reverse osmosis is slow and wastes a lot of water - for every litre of filtered water four or five litres go down the drain. They're also expensive to buy and run - the fragile membrane needs to be replaced regularly as it can become clogged or damaged and allow bacteria through.

Reverse osmosis filters won't remove THMs and some are damaged by chlorine.

Distillation

A distiller boils the water then condenses the steam, leaving impurities behind. Distillation removes most contaminants, including bacteria and protozoan cysts. It won't remove volatile organic compounds such as THMs unless it is combined with a carbon filter.

A distillation system is expensive to buy and run as it uses quite a bit of electricity. It's also slow and takes up a lot of room on your bench.

Home water treatment options