Filtration technologies and filter processes at a glance - What is filtered with what?

Water filters are generally used to make our water clean and tasty. Despite the German Drinking Water Ordinance, harmful substances can still be found in drinking water. ^[1]

There are a number of different filtration technologies that purify our water using various filter processes. It's no wonder that it's easy to lose track.

In this article, we will therefore explain...

• ... which filtration technologies (or water filters) are available, 
• ... which filter process these technologies are based on, 
• ... and which substances you can reduce from drinking water with which water filter.

Filtration technologies and where they are used

There are now a wide variety of filtration technologies on the water filter market. They all make use of various filtration processes and aim to make our drinking water as pure as possible. The best-known filtration technologies include 

• Activated carbon filter
• Reverse osmosis
• Ion exchange filter
• Distillation

Activated carbon filter

One of the most widespread and oldest filter technologies is activated carbon. This filter medium is used either as granulate or in block form.

Table or jug filter

This type of activated carbon filter usually uses poured loose activated carbon granulate. The granulate filters both adsorptively and catalytically, but less mechanically.

Due to its porous, friable structure, activated carbon has a very large surface area. As a result, it can also bind or convert dissolved substances such as chlorine or organic impurities that affect the taste and smell. 

What filters ...

Activated carbon block filter

Innovative activated carbon block filters are particularly efficient. These are pressed into a solid block in a state-of-the-art sintering process and activated at high temperatures. With this filter technology, the water pressure forces the water to penetrate the activated carbon filter, resulting in a significantly higher filter performance .

What filters ...

Reverse osmosis

The reverse osmosis treatment process was originally developed for the desalination of seawater. The process is relatively complex, but offers a high degree of purification of almost 99.9%. However, the efficiency is usually only between 70% and 99%.

Reverse osmosis water treatment reverses this process. Under pressure, the Tapwater is pressed against a semi-permeable membrane of the osmosis system with extremely fine pores. As only the water molecules themselves can pass through this membrane, all impurities are filtered out of the water.

However, reverse osmosis has one major disadvantage: almost everything is radically reduced from the water. This includes valuable substances such as minerals and salts. Although osmosis water can be drunk, it does not taste nearly as good due to the lack of minerals. In addition, the lowered pH value makes it acidic and therefore aggressive. For this reason, at least the minerals are often added artificially afterwards in order to obtain drinkable water. ^[3]

Tip

While reverse osmosis is useful in technical applications under controlled conditions (e.g. in medical technology and industry), it is rather unsuitable as a filtration method for household drinking water. A filter method that leaves the drinking water in its natural composition and structure makes more sense here. 

What filters ...

Ion exchange filter

What has already been described above for the table jug filter is also available as a large central system for the household: descaling systems that work with ion exchange technology. In this process, certain substances such as calcium and/or magnesium ions, which are responsible for water hardness, but also nitrates or heavy metals, are removed from the water and replaced by other ions. 

However, such ion exchanger systems are not actually real water filters. This is because microorganisms and most pollutants remain in the water (as is also the case with the table jug filter). 

What filters ...

• any specifically selected pollutant (e.g. nitrate, arsenic, sulphate)

• all other pollutants that were not specifically selected

Distillation

Water distillation, i.e. the evaporation of water with subsequent condensation, is one of the oldest ways of treating water. Both Tapwater and groundwater or contaminated water from natural occurrences can be distilled.

All pollutants and impurities, as well as minerals, trace elements and salts, are removed from the water. Distilled water is mainly used as a solution in chemistry, medicine and biology. 

However, distillation is a very energy-intensive and therefore quite expensive process (approx. 15 to 20 cents per liter). It also takes a very long time - an 800 watt appliance needs around 4 to 5 hours to distil 3 liters of water.

What filters ...

• approx. 99% of all ingredients and pollutants (incl. nitrate and lime)

• approx. 1% of dissolved substances

Different filter methods and what is filtered with them

In principle, the various filter methods can be divided into two large groups: 

• Process that reduces certain substances from the water due to chemical-physical effects. These include the catalytic and adsorptive filter effect.
• Purely mechanical filter processes that function like a sieve and retain substances due to their pore size.

Catalytic filter process

A catalytic filter effect is achieved by converting substances in the water using activated carbon or ion exchangers. With this type of filtration, no chemicals need to be added and the balance of the water is not altered.

Example

The catalytic filter process can be used to convert the hardness formers magnesium and calcium into larger crystalline limescale clusters. Although calcium and magnesium remain in the water, they no longer form limescale deposits. As a result, the water is softened.

The catalytic filter process allows a range of different substances to be filtered out of the water: 

• Chlorine and various chlorine compounds
• Heavy metals
• Nitrate
• Sulfates

• Pesticides
• Arsenic
• Iron

Adsorptive filter process

Adsorption is a physical process in which substances (usually molecules) adhere to the surface of another substance (e.g. activated carbon) and accumulate there. In the case of water filters, an adsorptive filter effect is achieved by certain substances in the water adhering to or being sucked in by the surface of the activated carbon like a magnet.

As this adsorptive effect works independently of the pore size, inorganic and organic substances that are smaller than the actual pores and channels are also retained. However, the water remains in its natural form, including all valuable minerals, salts and lime.

Substances reduced by adsorption are

• Heavy metals
• Herbicides
• Pesticides
• Fungicides

• Hormones
• Drug residues
• Odor- and taste-disturbing substances

Mechanical filter process

A mechanical filter works according to the principle of a sieve. All solids that are larger than the pores of the sieve (= filter fill or membrane) are retained or filtered out.

The pore size is relevant for the effectiveness of the water filter. This is because it indicates which substances are filtered and which remain in the drinking water. In principle, the pore size of the water filter must always be smaller than the pore size of the substances that are to be filtered out of the water.

A distinction is made between different filtration areas based on the pore size.

• Microfiltration: Separation of particles with a pore size of up to 0.2 µm
• Ultrafiltration: Separation of particles with a pore size between 0.1 and 0.01 µm
• Nanofiltration: Separation of particles with a pore size between 0.01 and 0.001 µm
• Reverse osmosis: Separation of particles with a pore size between 0.01-0.001 µm and additionally monovalent ions

• Sand
• Floating parts
• Rust particles
• Asbestos fibers

• Microplastics
• Bacteria
• Viruses

Conclusion about filter media: quality is the be-all and end-all

Filtration technologies and filter processes go hand in hand and together try to guarantee water that is as clean and pollutant-free as possible. The filter performance of the different water filters varies greatly and always depends on the quality of the product.

A good example of this is the activated charcoal filter: a filter in which the activated charcoal is only loosely piled up will never achieve the performance of an elaborately produced activated charcoal block filter. First-class activated charcoal filters differ in that the activated charcoal is not granulated or glued together with binding agents to form a mass, but sintered under high pressure and heat. As a consumer, you should therefore always pay attention to which manufacturing process is used.

If you want to filter your drinking water, you should also think carefully in advance about which substances you want to filter out of the water. This is because there are very big differences depending on the filtration technology and process used.

FAQs

Related articles and products