The purpose of a filter system is to eliminate pollutants from water such as sediment, hardness, chemicals, bacteria and viruses, resulting in cleaner, better-tasting drinking water. You can use this water for drinking, or more specialised purposes like brewing coffee, cooking and making crystal clear ice without worrying how it would affect your health.
The 5 Types of Filters
1. Reverse Osmosis
The method of eliminating dissolved inorganic particles (such as magnesium and calcium ions) from water by forcing it through a semipermeable membrane under pressure so that most of the pollutants are left behind is better known as reverse osmosis (RO).
Easy to use reverse osmosis water filtration systems are a highly effective method of water purification that is frequently paired with other filters such as a mechanical (sediment) and an absorption (activated carbon) filter to return water with few pollutants remaining.
This type of water filter uses water pressure to force water through the membrane, thus it does not require energy, though some waste of water is produced and must be disposed of. The additional filters required in multi-stage water filtration can make a reverse osmosis unit more expensive than other filtration methods, but it pays off especially for applications requiring 99.9% pure water.
2. Absorbent Filter
Carbon, which is particularly effective at absorbing water-borne pollutants, is most typically used for absorption in water filters. Carbon absorbs contaminants so quickly because it has a large internal surface that is densely packed with nooks and crannies that can trap chemical impurities like chlorine.
The majority of conventional household filters placed above their kitchen sinks use granular activated carbon (GAC), which absorbs unpleasant tastes and odours. More expensive types of water filter system contain carbon block components, which are generally more effective and usually have a particle removal rating in the micron range. Carbon filters can be made from a variety of materials, including wood and coconut shell, with the latter being the more effective yet also the more expensive option.
3. Isolating Filter
Sequestration is the chemical isolation of a material. In scale inhibiting filters, food-grade polyphosphate is typically used to sequester the calcium and magnesium minerals that produce limescale and corrosion.
Polyphosphate, on the other hand, is typically supplied at very small levels and just inhibits scale rather than eradicating it. This means that polyphosphate does not soften the water but rather helps to keep the minerals in the solution, preventing them from forming scale on any surfaces with which they come into touch.
Scale inhibition is not suitable for all applications due to the presence of hard minerals in the water. Water softening utilising a technique such as an ion exchange is typically indicated in places with alkalinity levels of 180ppm or more (extremely hard water) and applications where water is kept at a constant temperature of 95°C or higher.
4. Ion Exchange
Ion exchange is a method of softening hard water that involves exchanging magnesium and calcium ions in hard water for other ions such as sodium or hydrogen ions. In contrast to scale inhibition, ion exchange physically removes hard minerals, lowering limescale and making water appropriate for applications where a constant high temperature is maintained, such as in commercial coffee machines.
Ion exchange is most usually performed with an ion exchange resin, which is typically in the form of tiny beads. A similar type of resin is used in some water softeners, and in the case of a water softener, the resin uses sodium ions, which must be refilled regularly to keep the resin from becoming useless.
Because water filters are typically sealed units, you just replace the filter with a new one, however, Calcium Treatment Units (CTUs) can be returned to the provider and regenerated. Considering there are legal limitations to the quantity of salt (sodium) that can be present in drinking water, resins that employ sodium ions are not commonly used in drinking water filters.
5. Mechanical Filter
The primary principle of mechanical filtration is to use a barrier to physically remove sediment, silt, or other particles from water. Mechanical filters range from simple mesh filters that remove big trash to ceramic filters with exceedingly sophisticated pore structures that allow for ultra-fine filtration of harmful organisms. A filter that uses mechanical filtration is labelled with a micron rating which indicates how successful it is in terms of particle size removal.
Combination of Water Filtering Systems
Because each filtration method has limitations in terms of what it can remove, most water filtration systems employ a combination of processes to attain a certain level of water purity. Household water jug filters, for example, will normally utilise mechanical, absorption, and ion exchange, whereas inline filters will use mechanical and absorption, with the possibility of sequestration if the filter is constructed to inhibit scaling.
Depending on the number of stages in the reverse osmosis system, these systems can use mechanical, absorption, or both. Understanding the five basic techniques of water filtration and how they can be combined should make it easier to choose the type of filters you need for any specific application in your home.