Water Softener Filters
Water filters are devices used to take out contaminants from the water supply - mostly for drinking purposes only. Only 1 to 2% of the water supplied to a home is used for drinking and cooking, the rest is used for flushing toilets, bathing, laundry, etc. So water filters are usually located or installed at or under the kitchen sink. Different types are available: jug filters, activated carbon filters, reverse osmosis and distillation. Because the application is for drinking only, the volume of water produced is low. They do not affect scale in the heating system, scum on sanitary fittings or soap and detergent usage.
Activated Carbon Filters
The majority of water filters sold use activated carbon in one form or another. Activated carbon is made by carbonising various natural materials like coal or coconut shell and then steam treating it to activate its high surface area. It is made in granular, powder or porous block form and then made into a cartridge for inclusion within a water filter. When water passes through the carbon, organic contaminants are adsorbed onto the high surface area. It will also reduce chlorine - and, as organics and chlorine are the main causes of complaint about the taste, odour and colour of the water supply, activated carbon filters are very popular for treatment of water for drinking purposes.
The carbon is contained in a housing which is connected into the water supply usually under the kitchen sink. The treated water from the filter is then dispensed from a separate, dedicated drinking water tap on the sink. They are not generally used to treat the whole house supply.
Other Filter Media
Activated carbon filters are sometimes supplied in conjunction with other filter media, such as ion exchange resin (see water softener) which then adds the capability to reduce heavy metals or reduce scale in the kettle or coffee percolator or scum on tea or coffee.
The activated carbon cartridges eventually become exhausted and need to be changed. They are typically sized to treat 1000 to 2000 litres. Typically they need changing every 6 months or every year. It is important that this is carried out as otherwise water will not be effectively treated when it’s capacity is exhausted. Always follow the manufacturer’s instructions.
Jug filters have become very popular. A jug filter, as the name suggests, comprises a jug which is filled from the tap. The water then percolates from an upper compartment in the jug, through a cartridge filter into the lower compartment. The filtered water can be poured out as needed.
The jug filter cartridge usually contains activated carbon granules and an ion exchange resin to treat the water. The carbon reduces taste, odour and colour. The ion exchange resin is a specific type that reduces the temporary hardness from the water - so it reduces scale build up in the kettle and scum on tea or coffee - it does not take out all of the minerals.
Jug filters are intended for use in preparing drinks or cooking. They are not plumbed in to the water supply. They are best kept in the fridge. They are low cost and effective in improving the taste and aesthetics of drinks. They are of course low volume, need to be filled up regularly and the cartridge is small so it needs to be changed every month.
Reverse Osmosis or Membrane Filters
Reverse Osmosis (RO) filters use a particular type of membrane, through which water is passed to take out contaminants from the water. The membrane pores are extremely fine - so fine that they not only trap all particles or sediment, but many types and sizes of molecules (dissolved salts and minerals) as well. They produce almost pure water. This technology is also used to treat sea water to convert it into drinking water.
Because the membrane is so fine, the water flow through it is very slow - even with a high supply pressure. So the RO module has a very high surface area of membrane which is either spiral wound (like a toilet roll) or hollow fibre (hundreds of tiny straws clamped together inside a tube). Even then the flow is slow and a holding tank is usually necessary to provide a store of filtered water.
RO systems are usually plumbed into the water supply under the kitchen sink with a separate, dedicated drinking water tap.
They are provided with a pre-filter to prevent tiny particles clogging the fine membrane channels, and sometimes an activated carbon pre-filter to protect the membrane from attack by chlorine in the water supply. A carbon post-filter is normally used to help improve the taste.
Systems normally require regular annual maintenance to change the pre- and post-filters. Membranes typically last for 3 years or more.
During the reverse osmosis process the amount of water purified compared to the amount of water rejected and sent down the drain is in the order of 20 to 30% purified and 60 to 70% going down the drain.
This process separates the water from impurities by evaporating, cooling and condensation. When water is boiled the majority of the dissolved and particulate contaminants are concentrated in the boiling water and the steam is largely free from any contaminants. If the steam is then condensed, the condensed water is almost pure (rather like RO). Again, this process is used on a very large plant to desalinate sea water.
Like RO, the water produced is chemically very pure.