Water is one of the essential substances on the planet and plays a vital role in several applications, including agriculture, science, medicine, transportation, heating, recreating, and food processing. Most of us rely on drinking water from a treated municipal supply which is safe to drink but often has an unpleasant taste and odor. You may also find your mains water-causing limescale deposits that can block pipes and damage appliances depending on where you live.
Water filters are effective equipment that helps to remove unwanted contaminants such as sediment, taste, odor, hardness, and bacteria from water. There are different kinds of water filters on the market with ranging filter technology to help solve any number of water-related issues; Expwater explains the mechanism of 5 different water filters in the guide below.
Types Of Filters & How They Work
There are five main types of water filters, and they are:
- Mechanical Filters
- Absorption Filters
- Sequestration Filters
- Ion Exchange Filters
- Reverse Osmosis Filters
Each type of water filter is designed to address different water problems, and many filters even use a combination of these methods to offer more advanced filtration.
Mechanical filtration removes sediment, dirt, or any particles in the water by providing a physical barrier. Mechanical filters can range from providing a basic mesh to filter out large debris to ceramic filters with complex pore structures for ultra-fine filtration of pathogenic organisms.
Mechanical filters will usually be given a micron rating to indicate how effective they are in terms of particle size. Some of the common ratings you might encounter include:
5 micron – removes most particles visible to the naked eye
1 micron – removes particles that are too small to see without a microscope
0.5 micron – removes cysts like giardia and cryptosporidium.
Absorption filters often have carbon in their design as carbon is highly effective at capturing water-borne contaminants. This is because carbon has a huge internal surface that is jam-packed with tiny nooks and crannies to trap chemical impurities.
Most standard home filters contain granular activated carbon (GAC) to help reduce unwanted taste and odor through absorption. More expensive filters may have carbon block elements that are more effective and even carry a micron rating for particle removal.
Other than carbon, other substances that can be used in absorption filters include wood and coconut shells. Coconut shell filters are more effective, but they are also more expensive.
Sequestration is to chemically isolate a substance. Food grade polyphosphate is a common scale inhibitor that’s used in sequestration filters to sequester calcium and magnesium minerals in the water. However, polyphosphate is only introduced in small amounts, and they inhibit scale rather than eradicating it. This means that the filter doesn’t remove the minerals but only prevents them from forming scale on surfaces they come into contact with.
Since the hard minerals are still present in the water, scale inhibition isn’t the best choice for certain applications, in water areas with alkalinity levels of 180ppm or more, applications where water is kept at a constant temperature of 95 °C or more. It is recommended for you to use water softening processes such as ion exchange instead.
Ion Exchange Filters
Ion exchange is another chemical process that softens hard water by exchanging magnesium and calcium ions in hard water with other ions, like sodium or hydrogen. Unlike scale inhibition, ion exchange will reduce limescale by removing hard minerals.
Ion exchange is commonly carried out with an ion exchange resin that comes in small beads. The resin utilizes sodium ions that need to be recharged periodically to maintain the effectiveness of the resin. The water filters are usually sealed units and will need to be replaced regularly.
Resins with sodium ions aren’t suitable for drinking water filters as it means they introduce some amount of salt. However, drinking water is legally limited to 200 mg/L, and a hydrogen-based ion exchanger resin is recommended for drink water filters.
Reverse Osmosis Filters
Reverse osmosis removes dissolved inorganic solids like magnesium and calcium ions from water by forcing them through a semipermeable membrane under pressure so that water passes through while leaving behind most contaminants. This is a highly effective method to purify water and is usually combined with other filters such as mechanical and absorption to return water with little contaminants remaining.
Reverse osmosis uses water pressure to force water through the membrane, so it doesn’t need electricity, though it does produce a certain amount of wastewater to be sent to the drain. The extra filters involved also make a reverse osmosis unit more expensive than other filtration methods.