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Water filtration: what are the methods?

If you use water from your own sources, filtration is a necessary step that allows you to safely drink and use water at home. You may not know what types of water filtration exist, which water filter to choose and how to take care of it.

Chemical and mechanical water filtration

Drinking water filters differ according to technologies used, materials and use. Mechanical and activated carbon filters are the most common.

It needs to be emphasized that filtration means only getting rid of mechanical impurities from water. Mechanical filtration can either be screen or membrane. Membrane filtration is generally more efficient, but it is not suitable for drinking water - because the membrane also captures vital substances that our body would then lack. This method of filtration is therefore only suitable for technical usage, on the contrary, only a screen filter is used for home filtration of drinking water.

Chemical filtration is not filtration in the true sense of the word, but water treatment, in which undesirable chemical or organic substances are removed from the water. Granular activated carbon is most often used for these purposes, which, thanks to its surface and sorption properties, can capture a whole range of harmful substances dissolved in water - from heavy metals through chlorine and other chemicals to viruses and bacteria. Coal adsorbs or traps these substances and organisms on its surface. Thanks to this, it also removes unpleasant odors from the water and improves its taste, but it is not a complete substitute for water disinfection. In addition to coal, a wide range of other synthetic granules are used for water treatment.

Possible problems with mechanical impurities in water

Most people are well aware of the risks associated with microbial and chemical water pollution, but the risks of solid matter are less well known. Although small particles in the water do not pose a serious health risk to humans, they can slowly damage pipes and appliances, which then suddenly stop working. This is because mechanical impurities damage the inner surfaces, increasing the risk of limescale and cracks. In addition, they clog appliances such as washing machines and dishwashers.

Mechanical water filtration prolongs the life of water distribution systems and appliances.

Water contaminated with mechanical impurities does not have to be visibly turbid at all, often it is only an analysis of water that reveals the above-limit amounts. So mechanical filtration of well water is an essential part of all domestic waterworks. It should be used not only for drinking water, but also service (non-potable) water and water in the heating system.

In addition to households, mechanical water filtration is also used in agriculture (irrigation) and industry (cooling and technological water), where it ensures the reliability of technical equipment.

Mechanical water filtration principle

In the case of mechanical water filtration, a water filter with a fine screen is installed on the pipeline. Screens are usually made of durable polymer fibers. Filter catches the dirt and only clean water without mechanical particles (filtrate) flows through the pipes.

One basic parameter is the mesh density given in micrometers or microns (μm) and determines how much dirt a filter can capture. One micron is a thousandth of a millimeter, and home filters are typically 10-100 microns.

Density should correspond to the actual size of the undesirable impurities shown in your water analysis. Many people believe that the denser the screen, the more efficient water purification. But that is a mistake. Too dense screen causes lower water flow and more frequent need for cleaning. In addition, if the sieve is clogged, it catches even smaller dirt and becomes clogged faster.

Fibrous and elastic particles are problematic in this respect, for which the required mesh density cannot be determined unambiguously, since their permeability through the mesh is largely determined by water pressure and other parameters.

Combination water filter: how to assemble it?

As already mentioned, best results  are achieved by a combination of a screen and a activated carbon water filter, which can be connected into one system. For very polluted water, it should include a pre-filter, a water filter with a lower screen density. It catches the largest impurities, improving the filtration process, extending the life of the entire filtration system and reducing the need for cleaning and maintenance.

In the filtration system, the pre-filter (if installed) always comes first, followed by the fine screen filter. Other domestic water treatment plants operating on the basis of chemical reactions are also included, for example the mentioned carbon water filter or hard water filter. Proper placement is very important as mechanical impurities could degrade the carbon granulate.

SYR Ratio backwash filter. 

How to maintain water filters

In order for drinking water filters to work properly and not to clog (and block the water supply system), the screen must be backwashed regularly. Modern filters with automatic backwash function and control unit are completely maintenance-free - they monitor the screen condition, determine the need for rinsing and then automatically perform backwashing without your intervention.

Manual rinsing is more complicated, and you also have to monitor the condition yourself. The filter needs to be removed and the screen gently rinsed under running water until it is completely clean. A semi-automatic solution is a water filter with a backwash function. In this case, you do not have to remove the filter, you just open the valve to start backwasing, from which water then flows out, even with dirt from the sieve.

In activated carbon filters, it is necessary to regularly change the filter cartridge, which has a limited life of about 6 months. At the end of its service life, coal loses its adsorbtion properties and is unable to effectively remove unwanted substances from water.