Water Filters remove unwanted impurities from water such as sediment, taste and odour, hardness and bacteria to result in better quality water. From producing better-tasting drinking water to more specialist applications such as brewing coffee and making crystal clear ice, we offer a huge range of filters and cartridges to solve any number of water-related issues.
The 5 Types of Filters
Subject to your application, what you’re trying to remove or in some circumstances trying to stop, there are 5 types of water filters:
Ion Exchange Filters
Reverse Osmosis Filters
Many filters actually use a combination of these methods to perform multiple levels of filtration.
Water is vital to a huge number of applications including agriculture, science, medical, transportation, heating, recreation and food processing as well as washing and the most important of all: drinking.
Drinking water comes from a treated municipal supply which is safe to drink but will often feature unpleasant tastes and odours from chemicals such as chlorine which are used to disinfect the water and keep it free of germs and bacteria. Depending on where you live, you may also find that your mains water causes limescale deposits to form which can block pipes and damage appliances. These issues are just two among a host of other common water problems which can be solved by water filtration.
The basic idea of mechanical filtration is to physically remove sediment, dirt or any particles in the water using a barrier. Mechanical filters can be anything from a basic mesh that filters out large debris to a ceramic filter which has an extremely complex pore structure for ultra-fine filtration of pathogenic organisms.
A filter that utilises mechanical filtration will usually be given a micron rating which indicates how effective the filters are in terms of the size of the particles it is capable of removing. Common ratings you might see include:
5 micron - Will remove most particles visible to the naked eye.
1 micron – Will remove particles which are too small to see without a microscope.
0.5 micron - Will remove cysts (giardia and cryptosporidium).
Absorption in water filters is most commonly carried out by carbon, which is highly effective at capturing water-borne contaminants. The reason carbon absorbs contaminants so readily is that it has a huge internal surface which can trap chemical impurities such as chlorine.
Most common domestic filters contain granular activated carbon (GAC) which reduces unwanted tastes and odours by absorption. More expensive filters use carbon block elements which are generally more effective and usually carry a micron rating for particle removal.
Sequestration is the action of chemically isolating a substance. Food grade polyphosphate is commonly used in scale inhibiting filters to sequester the calcium and magnesium minerals which cause limescale and corrosion. Polyphosphate is generally only introduced in very small amounts and it only inhibits scale rather than eradicating it. This means that polyphosphate does not soften the water but instead works to keep the minerals within the solution, preventing them forming as scale on any surfaces they come into contact with.
Due to the hard minerals still being present in the water, scale inhibition isn’t suitable for all applications in contrary water softening using a process such as ion exchange is usually recommended in water areas with alkalinity levels of 180ppm or more and applications where water is kept at a constant temperature of 95°C or more.
Ion exchange is a process used to soften hard water by exchanging the magnesium and calcium ions found in hard water with other ions such as sodium or hydrogen ions. Unlike scale inhibition, ion exchange physically removes the hard minerals, reducing limescale and making water suitable for applications.
Ion exchange is most commonly carried out using an ion exchange resin which normally comes in the form of small beads. A similar type of resin is used in some water softeners and in the case of a water softener the resin utilises sodium ions which need to be periodically recharged to prevent the resin becoming ineffective.
Resins that utilise sodium ions aren’t usually used in drinking water filters as the amount of salt that can be present in drinking water is legally limited to 200 milligrams/litre. As sodium ion exchange increases salt levels.
Reverse osmosis is the process of removing dissolved inorganic solids (such as magnesium and calcium ions) from water by forcing it through a semipermeable membrane under pressure so that the water passes through but most of the contaminants are left behind.
Reverse osmosis is a highly effective way of purifying water and is usually combined with a number of other filters such as a mechanical (sediment) filter and an absorption (activated carbon) filter in order to return water with few contaminants remaining.
RO systems use water pressure to force water through the membrane so it uses no electricity, though a certain amount of waste water is produced that has to be sent to the drain. The extra filters involved in multi-stage water filtration can make a reverse osmosis unit more expensive than other filtration methods but in applications where 99.9% pure water is required, RO offers the finest level of filtration available.