Cartridge filters

Cartridge filters are simple, modular filters, and can be used to remove particles, or sometimes chemicals, from your water.

They work by trapping solid material in the water. The filter will remove particles of above a certain size. The filter should be clearly marked with its size rating.

For many supplies, several filters in descending order of particle removal size will be needed. The exact choice depends on the quality of the supply and the substance(s) that need to be removed.

As long as they're installed and used correctly, cartridge filters can remove sediment, metals and some microorganisms from the water.

You should make sure that the filters are correctly sized for your water flow, otherwise they may get blocked.

Cartridge filters work best where there is not much solid material in the water supply and little manganese or iron (less than about 300 microgrammes per litre of iron).

You may need to use filters containing loose media if there's a significant quantity of sediment in the water, or high concentrations of iron and manganese.

Some filters have carbon in them to remove low concentrations of the organic compounds that cause colour in water.

Installing cartridge filters

Correct installation depends on your individual circumstances. So it may be best to consult a specialist contractor, otherwise you risk the filters not being effective, or blocking.

Choose filters that are approved by the Water Regulatory Advisory Scheme or NSF, the national public health and safety organisation.

Replacing cartridge filters

Cartridge filters need to be replaced once they become dirty or blocked.

How often they need to be changed depends on the quality of the water passing through them, and should be decided for each supply.

It's best to keep stocks of spare cartridge filters in case you need them. To change a filter:

• turn the supply off
• unscrew the housing
• empty any water inside the housing
• carefully replace the filter, taking care to achieve a good seal

If you're changing your filter, take care not to contaminate the new filter and dispose of the old one carefully.

There could be health risks associated with handling dirty filters, because bugs can be trapped in their debris.

Follow the manufacturer's instructions for your filter if you have them.