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The process of osmosis is a fascinating natural phenomenon in which pure water migrates through seemingly impermeable cell walls to dilute high concentrations of dissolved substances. Space scientists have been able to synthesize such "walls" and, in reverse, use water pressure to separate dissolved substances from the water. This has developed a filtration process that removes all conceivable contaminants in water extremely effectively. But how exactly do water filters work using this process, and when is such a filter worthwhile for me...?
Don't want to miss out on clean, healthy drinking water at home? With the help of a reverse osmosis system, you can obtain pure drinking water that is 85-97% free of all dissolved contaminants, as well as pollutants.
But what exactly is reverse osmosis? How do reverse osmosis systems actually work? How do I purify my drinking water with a reverse osmosis water filter? What ongoing costs will I incur when changing the filter? Here you'll learn everything you need to know about reverse osmosis systems.
There are various filtration processes for purifying water. In addition to modern activated carbon block filters like those from CARBONIT and steam distillation, there is reverse osmosis, a filtration process based on the process of osmosis.
To understand how reverse osmosis systems work, it's important to first understand the process of osmosis: Osmosis is a process that occurs between two unequally concentrated solutions. Water molecules in an aqueous solution tend to pass through a semipermeable membrane from a less concentrated solution to the more concentrated one. Such membranes (in organisms, for example, cell walls) naturally strive to equalize salt concentrations by diluting the more concentrated side with water.
In the normal osmosis process, the so-called osmotic pressure acts toward the more concentrated solution. If a pressure far exceeding the osmotic pressure is available, this natural process can be reversed (reverse osmosis). In reverse osmosis, the water molecules pass through the membrane from the more concentrated side to the less concentrated side. To prevent solids from accumulating on the membrane, the concentrated water is slowly and continuously rinsed off and discharged into the wastewater.
Water treatment using a reverse osmosis system makes use of the natural phenomenon of osmosis “in reverse” to free contaminated water from pollutants and other undesirable foreign substances (e.g. limescale).
All reverse osmosis systems operate according to the reverse osmosis filtration process. Water is forced through the membrane by applying a typical line pressure of 3-6 bar.
In other words, practically only the water molecules pass through the fine pores of the membrane, whereas 85-97% of the dissolved foreign substances and pollutants remain behind and are flushed into the wastewater.
Reverse osmosis is considered the most delicate filtration process available for purifying water. During the pressurized production process, reverse osmosis water filters allow only H2O molecules and a very small number of dissolved ions to pass through.
A reverse osmosis system can filter limescale and other dissolved minerals, nitrate/nitrite, bacteria, organic compounds, chlorine and chlorine degradation products, drug residues, pesticides, all metals and heavy metals, as well as asbestos fibers and microplastics from your drinking water. 
You're probably familiar with tabletop or pitcher filters: The water is poured into the top of the pitcher for filtering, and it drips into a reservoir. The main components of the filter elements, at approximately 90%, are cation exchange resins (a plastic resin) and activated carbon granules. The goal of these systems is to remove as much of the calcium and magnesium from drinking water as possible (this makes black tea clearer and prevents the formation of tea skin!). In return, another cation (often a hydrogen compound) is released. In short, these systems make almost exclusively cosmetic changes to drinking water and are not intended to specifically remove contaminants.
A simple water filter isn't sufficient to filter out pharmaceutical residues, uranium, or pesticides from water, for example. Reverse osmosis systems, on the other hand, are characterized by very good pollutant retention and are also suitable for treating (heavily) contaminated water.
Filtering through reverse osmosis systems almost completely purifies tap water, and osmosis water also provides the basis for numerous forms of treatment. However, the fact that reverse osmosis removes all of the water's constituents, including minerals, is often cited as a disadvantage of reverse osmosis systems.
Whether minerals contained in water can even make a significant contribution to nutrient requirements is controversial. To meet their daily magnesium and iron requirements by drinking water, a person would need to consume approximately 50 liters of water. It stands to reason that a balanced diet is the most likely and much easier way to meet mineral needs.
Some physicians and nutritionists now recommend drinking low-mineralized water, which is also commercially available, due to its beneficial detoxifying effects. Drinking this water, even long-term, poses no risks.
Use reverse osmosis water for more than just drinking (pure, ice cubes, beverages) and cooking! The pure water has many uses...
Reverse osmosis and baby food: Unlike adults, babies have a particularly hard time filtering and excreting harmful substances through their kidneys. Therefore, parents should give their babies water with very low mineral and contaminant loads. Reverse osmosis water is therefore ideal for preparing baby food.
Reverse osmosis water for plants : Too much lime in the water leads to chlorosis. This condition occurs in most houseplants, whose absorption of iron, minerals, and other nutrients is impaired by calcareous water.
Reverse osmosis glass cleaning : Reverse osmosis systems and osmosis water are suitable for cleaning and rinsing glass. After rinsing and cleaning, osmosis water leaves no trace of water stains, such as those caused by hard water.
Reverse osmosis water for aquariums: Pets and animals also benefit from using a reverse osmosis system . Reverse osmosis is particularly useful for aquarium owners. The mixture of pure reverse osmosis water and tap water creates optimal water parameters for many fish species.
It's not always easy for prospective buyers to find a reverse osmosis system that meets their individual needs. If you're considering purchasing a reverse osmosis system for your home, there are a few things to consider:
When purchasing a reverse osmosis system, make sure it has a fine filter or pre-filter . A fine filter should always be installed upstream of the reverse osmosis membrane to prevent particles sometimes found in drinking water from clogging the membrane.
Since membrane quality determines the performance of your reverse osmosis system, your osmosis system should be equipped with a high-quality osmosis membrane. H2O systems exclusively use polyamide/polysulfone membranes . This is because this type of membrane has proven itself in thousands of drinking and pure water treatment plants and industrial facilities worldwide. These membranes are currently unmatched in terms of retention rates and yield.
When purchasing a reverse osmosis system, competent advice and good service throughout the system's lifetime are particularly important. Only reliable and objective advice can help you find the right reverse osmosis system for your individual needs. The sales staff should be highly trained and experienced to ensure the high quality of advice. Furthermore, you should not rely on the replacement service offered by direct salespeople. Such distributors usually only exist for a few years and are often no longer able to supply you with the filters you need afterward. Furthermore, they often charge hefty fees for filter replacement.
When purchasing a reverse osmosis system, make sure the manufacturer is based in Germany and that you have a reliable contact person. We at H2O are happy to advise you nationwide or directly in our flagship store in Berlin .
Despite optimized membrane surface areas, conventional home filter systems typically only produce approximately 3 to 10 liters of pure water per hour. This flow rate of approximately 50–170 ml per minute is often insufficient for everyday use. These household systems therefore require a storage tank and a dedicated faucet.
Don't be fooled: "Fast" doesn't necessarily mean "good" when it comes to reverse osmosis technology. The less downtime a system has (because it operates very slowly), the longer its lifespan and the better the filtration quality.
There are three solutions available for the convenient application and use of reverse osmosis:
With this type of device, the purified water is piped through the under-counter units into a (storage) pressure tank. A separate filter tap (or a 3-way tap) allows you to withdraw the collected purified water as needed at a pressure of approximately 1–2 bar. The amount of purified water that can be stored depends on the size of the storage tank . The standard capacity is approximately 4 L (small) or approximately 10 L (large). 
The first reverse osmosis water filters or reverse osmosis systems for the home were countertop units with a connection adapter for the kitchen faucet. They essentially function the same way as pressure tank systems, with the only exception being that both the filter unit and the storage tank are located on the countertop. The water, freed of impurities and contaminants, is piped into collection tanks and can be drawn off as needed using a tap.
There are now even systems that operate entirely without a faucet connection, for example, from the Korean company Hurom/Dahlert. A current model from Hurom, which supplies both warm and hot pure water in addition to pure water, is scheduled to be available from March 2025.
In addition to tank systems, there is also the so-called Direct Flow reverse osmosis system. The reverse osmosis system in the pressure tank models automatically produces osmosis water and stores it in a storage tank. The Direct Flow reverse osmosis system, on the other hand, produces osmosis water in real time.
The Directflow reverse osmosis system therefore works entirely without an intermediate tank. It provides you and your household with reverse osmosis water at the touch of a button, thanks to its high performance as an under-sink reverse osmosis system. However, with the simpler models – such as the Rowa OneFix or TwoFix – you should consider whether the produced volume of 200 to 400 ml per minute meets your comfort requirements before making a decision.
The Rowa Sirius delivers 1–1.5 liters per minute, but requires an electric pressure booster and a very large membrane. This sophisticated technology comes at a price...
To ensure your reverse osmosis system functions properly, you should replace the post-filter approximately every 12 months. The pre-filter should be replaced approximately every six months, depending on the quality of the raw water.
Depending on the reverse osmosis system model, the cost of filter cartridges varies. For our H2O Economy 3+ blue reverse osmosis water filter, the annual cost of replacing the pre- and post-filters is calculated as follows:
Pre-filter 5" Eco PP (change interval approximately every 6 months): 12.50 EUR
Post-filter IFP Select-5 SOE (change interval approximately every 12 months): 25.00 EUR
Extrapolated over a year, the cost of replacing the filter cartridges is approximately EUR 50.
With our filter subscription, you'll also save 10%. Click here to fill out the H2O filter subscription form .
With regular prefilter changes, the membrane can operate for a very long time without deterioration – on average, 3 to 5 years. Replacing the reverse osmosis membrane costs around €110. You can also perform this maintenance yourself. A quick tip: It's worth replacing the flow restrictor at the same time to ensure the new membrane is reliably flushed for a long time.
Every 5 years it is also worth investing in a new storage tank.
During long downtimes and poor conditions (heat, contaminated raw water), bacteria can penetrate the osmosis membrane ("grow through"). To prevent bacteria from settling on the pure water side of the reverse osmosis system, the system can be regularly disinfected as a preventative measure.
To effectively disinfect the reverse osmosis system, including the tank, you can use hydrogen peroxide (e.g., ROWAper 7.5%). Tip: Disinfect your reverse osmosis system when changing the filters. It's best to disinfect the system before installing the new filters.
How do I clean the reverse osmosis system?
There are various ways to filter water. As an alternative to reverse osmosis water filters, water can also be filtered using the following technologies:
These water filters only serve to improve the taste. They do not remove heavy metals or drug residues. Furthermore, there is a risk of microbial contamination.
Activated granular filters are widely used in America to remove chlorine. However, these filters also only partially remove heavy metals and pharmaceutical residues. These systems tend to promote the growth of germs, which is why the activated carbon is often silvered. Some of the silver is also released into the filtered water.
Since these systems are not designed to specifically remove pollutants from drinking water, they are not available from H2O.
Modern activated carbon block filters like those from Carbonit have been proven to remove heavy metals, asbestos, herbicides, pesticides, drug residues, hormones, bacteria, and much more from drinking water. We recommend this type of filtration to anyone who wants to remove contaminants from their drinking and cooking water and is otherwise willing to accept existing water hardness.
In our opinion, a German manufacturer of activated carbon block filters is particularly recommended for high-quality drinking water filters: CARBONIT Filtertechnik GmbH.
We offer the following CARBONIT drinking water filters in our shop:
Reverse osmosis filters out 99–100% of all organic matter and 85–97% of dissolved substances from the water. A reverse osmosis system for your home allows you to drink low-mineralization (good for detoxification!) and contaminant-free water whenever you need it.
There is no danger from drinking this low-mineral water, even with long-term use (it's similar to fresh rainwater). This is because humans absorb most of their minerals through food, juices, and teas. The body needs good drinking water that is free of foreign substances and pollutants, especially as a means of transportation and cleaning.
To ensure consistently clean drinking water and the longevity of your reverse osmosis system, you should maintain it regularly (changing pre- and post-filters). Preventative disinfection provides protection against contamination if your system is frequently down for extended periods.
As an alternative to reverse osmosis, you can also use CARBONIT's high-quality activated carbon block filters for effective water filtration. The patented technology of CARBONIT's high-performance activated carbon block filters demonstrably and reliably removes many undesirable substances from the water and is TÜV-certified for bacteria-free properties.
If you have any questions about reverse osmosis or our reverse osmosis systems, please feel free to contact us . We would also be happy to advise you on our other products – always individually, objectively, and professionally!
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