Water filtration: what methods are there?

If you draw water from your own sources, filtering it is a necessary step to enable you to consume and use it safely in the home. But do you know what types of water filtration there are, what to choose a water filter for, and how to maintain it?

Chemical and mechanical water filtration

Drinking water filters vary according to the technology, filter materials and purpose. The most common are mechanical and activated carbon filters.

At the outset, it should be emphasized that filtration means only the removal of mechanical impurities from water. Mechanical filtration can be sieve or membrane filtration. Membrane filtration is generally more efficient, but is not suitable for drinking water – the membrane also traps vital substances that the organism would then lack. This method of filtration is therefore only suitable for technical purposes, whereas a sieve filter is used exclusively for home filtration of drinking water.

Chemical filtration is therefore not filtration in the true sense of the word, but water treatment, whereby undesirable chemical or organic substances are removed from the water. Granular activated carbon is most commonly used for this purpose and, thanks to its surface and sorption properties, can capture a wide range of harmful substances dissolved in water – from heavy metals to chlorine and other chemicals to viruses and bacteria. Carbon absorbs or traps these substances and organisms on its surface. It also removes unpleasant odours and improves the taste of the water, but beware, it is not a full-fledged substitute for water disinfection. In addition to charcoal, a wide range of other synthetic granules are used for water treatment.

Risks of mechanical impurities in water

While most people are well aware of the risks associated with microbial and chemical contamination of water, the risks of particulate matter are less well known. Although small particles in water do not pose a serious health risk to humans, they can subtly damage pipes and appliances which then suddenly go out of service. This is because mechanical debris erodes the internal surface of the pipes, 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 plumbing and appliances.

Water with an admixture of mechanical impurities at all need not be visibly turbid, often only a water analysis will reveal the presence of impurities above the limit. Mechanical filtration of well water is therefore an essential part of all domestic waterworks. It should be used not only for drinking water, but also for service water and water in the heating system.

In addition to households, mechanical water filtration is also used in agriculture (irrigation water) and industry (cooling and process water), where it ensures trouble-free operation of technical equipment.

The principle of mechanical water filtration

In the case of mechanical water filtration A water filter with a fine screen is installed on the pipe through which water flows. The sieves are usually manufactured from fibres made of a durable polymer. The filter captures the impurities and clean water without mechanical particles, or filtrate, continues to flow.

The basic parameter in the selection of a mechanical filter is fineness of the sieve. This is given in micrometers or microns (μm mark) and determines how much dirt the filter can trap. One micron is one thousandth of a millimetre and household filters typically use a screen fineness of 10-100 microns.

The fineness of the sieve should correspond to the actual size of the unwanted impurities revealed by the water analysis. Many people believe that the denser the screen, the more effective the water purification will be. This, however, is a mistake. Too dense of a screen causes lower water flow and more frequent need for cleaning. In addition, if the strainer is clogged, it will also trap smaller debris and clog more quickly.

Problematic in this regard are fibrous and elastic particles, for which the desired sieve density cannot be determined unambiguously, since their passage through the sieve is largely determined by water pressure and other parameters.

Combined water filter: how to build it?

As we have already mentioned, the best results in the home are achieved by combining a mesh and carbon water filter, which can be combined into one system. In the case of highly polluted water, it is advisable to include a so-called pre-filter, i.e. a water filter with a lower sieve density, in the combined filter. This will trap the largest impurities, thereby making the filtration process more efficient, extending the life of the entire filter system and reducing the need for cleaning and maintenance.

In a filtration system, the pre-filter (if installed) is always first, followed by the fine screen filter. Next in order are other domestic water treatment systems operating on the basis of chemical reactions, such as the aforementioned carbon water filter or hard water filter. Correct sorting is very important as mechanical impurities could degrade the carbon granulate.

How to maintain water filters

In order to keep drinking water filters working properly and prevent them from clogging (and thus clogging the water system), it is necessary to sieve periodically clean by flushing. Modern filters with an automatic flushing function and a control unit are completely maintenance-free in this respect – they can assess the level of clogging of the sieve, determine the need for flushing and then automatically perform the flushing without your intervention.

Manual flushing is more complicated, and you have to monitor the sieve condition yourself. The entire filter must be deinstalled and the sieve gently rinsed under running water until it is completely clean. A semi-automatic solution is a water filter with backwash function. In this case, the filter does not need to be deinstalled, the backwash is triggered by opening the backwash valve, which then drains the water and dirt from the sieve.

In activated carbon filters, regular flushing is required. replacement of the filter cartridge, which has a limited life of approximately 6 months. At the end of its useful life, coal loses its sorption properties and cannot effectively remove undesirable substances from the water.