What Is Reverse Osmosis? Functionality and Applications

What is reverse osmosis?

Reverse osmosis, also known as reverse osmosis, is a physical process for concentrating substances dissolved in liquids, which uses pressure to reverse the natural osmosis process. This process is used primarily for water treatment. A reverse osmosis system is a water filter that removes all foreign substances from tap water. These include drug residues, pesticides, microplastics and other pollutants.

Reverse osmosis was originally developed for military and space travel to make wastewater safe to drink. Today, it is used in various areas:

• Drinking water treatment: Purification of tap water for domestic use.
• Wastewater treatment: Treatment of waste water to make it reusable.
• Aquarium water: Treatment of water for aquariums.
• Manufacture of fruit juice concentrates: Application in the food industry.

Reverse osmosis systems are primarily designed to treat municipal tap water, but can also be used with other water sources as long as the correct pre-filters are available.

Why is reverse osmosis important?

Reverse osmosis is important to improve the quality of your drinking water and free it from pollutants. Originally developed for wastewater treatment, reverse osmosis is now used primarily to detoxify tap water. Even in Germany and Europe, where water is considered “good”, contamination by ultrafine particles such as PFAS is a growing problem.

Wastewater treatment plants can no longer adequately remove many of these pollutants, including drug residues. Every day, large quantities of expired drugs enter wastewater, which decompose and leave behind dangerous residues. These drug residues are particularly critical because they were developed so that the body absorbs them quickly.

Another problem is the over-fertilization and acidification of soils due to intensive agriculture. As a result, high amounts of nitrite and nitrate get into groundwater and pollute the drinking water cycle. Large-scale use of pesticides and fungicides also contributes to the deterioration of water quality.

The reputation of “good” water in Germany is mainly due to limited water analyses. These analyses only take into account a limited number of ingredients, as more comprehensive testing is complex. In addition, limit values for pollutants in drinking water are adjusted as needed, which conceals the actual load.

It is therefore advisable to independently purify the drinking water by means of a reverse osmosis system. The system is installed at the end of the waterway, i.e. after your house pipes, and removes any remaining contaminants itself.

Basics of reverse osmosis

In reverse osmosis, water is forced through a semi-permeable membrane to remove contaminants such as salts, bacteria, and chemical pollutants. To understand the basics of this process, let's look at the natural principles of osmosis and its reversal through reverse osmosis.

Osmosis — The natural principle

Osmosis is a natural process in which liquids are separated by a semi-permeable membrane. This membrane only allows certain molecules, usually water, to pass through, while other substances, such as salts and larger molecules, are retained. In nature, concentration balance is achieved in this way. For example, dissolved salts on one side of the membrane attract water molecules from the region of lower concentration. This effort to balance concentration is referred to as osmotic pressure.

A well-known example is the bursting of cherries in late summer: Osmotic pressure causes water to flow into the fruit until the increased pressure causes them to burst. This process is omnipresent and influences biological and physical processes in our daily lives.

The concept of reverse osmosis

In contrast to natural osmosis, reverse osmosis uses targeted pressure to reverse the natural concentration balance. Here, the raw water is pressed onto one side of the membrane. Because the pressure applied is higher than the osmotic pressure, the water is pushed across the membrane while the solutes are retained.

• How does reverse osmosis work?: Raw water that contains impurities is pressed onto one side of the semi-permeable membrane. The pressure exerted on the raw water must be higher than the natural osmotic pressure. In this way, the water molecules are pushed through the membrane into the region of lower concentration, while most solutes remain behind. This clean water is then removed as osmosis water. The remaining contaminants, the so-called concentrate, are removed continuously to prevent crystallization and clogging of the membrane.
• Difference between osmosis and reverse osmosis: While in natural osmosis, the concentration balance takes place automatically by diffusing water from the pure side to the contaminated side, in reverse osmosis, the process is reversed. A pressure that is higher than the osmotic pressure is exerted on the contaminated side. The water flows through the membrane and the dissolved contaminants remain behind.

Osmotic pressure and its significance

Osmotic pressure is the decisive factor in reverse osmosis. It describes the pressure that is necessary to prevent the natural balance of concentration.

• Osmotic pressure in drinking water: Drinking water generally has an osmotic pressure of less than 2 bar. In the case of reverse osmosis of drinking water, the pressure used must be at least 3 to 30 bar, depending on the membrane and the system configuration.
• Osmotic pressure in seawater and other media: Due to its high salt content, seawater has an osmotic pressure of around 30 bar. Reverse osmosis to desalinate seawater therefore requires a pressure of 60 to 80 bar. In extreme cases, such as when treating landfill leachate, even higher pressures may be required.
• Pressure requirements in reverse osmosis: The osmotic pressure increases as the difference in concentration increases. However, when the pressure difference equals the osmotic pressure, the process comes to a standstill because an osmotic equilibrium has been reached. To maintain the process, the concentrate must be removed continuously. This is done using pressure regulators or pressure exchangers, which reduce operating costs through energy recovery. The energy consumption for reverse osmosis is 4—9 kWh per cubic meter of water.

Historical development of reverse osmosis technology

Reverse osmosis was originally developed for military and space applications to treat wastewater into drinking water. Since then, the technology has continued to develop through innovation and is now widely used in drinking water treatment, seawater desalination and industrial water treatment. Thanks to the use of ever better membranes and more efficient pressure systems, reverse osmosis is now one of the most effective methods for producing almost 100% pure drinking water.

Technical details of reverse osmosis

Components of a reverse osmosis system

A reverse osmosis system consists of several essential components that enable thorough water purification. The main elements are pre-filter, membrane, post-filter, as well as a water tank and a pressure pump.

Before installation, it is crucial to carry out pre engineering to determine the water quality and pressure requirements of the system components. Basic and detail engineering is then of great importance when selecting the appropriate membrane and prefilter to ensure optimum filtration performance.

Prefilter: The pre-filter is placed in front of the reverse osmosis membrane. His job is to pre-purify tap water by removing coarse particles and contaminants. This protects the sensitive membrane from unnecessary wear and ensures that it reaches its full lifespan. The pre-filters are crucial to remove sediment, chlorine and other major pollutants from water before it enters the sensitive membrane. There are different types of prefilters:

• Sediment filter: These remove larger particles such as sand, rust and dirt from the water. They act as a protective barrier for the membrane by preventing gross contaminants from entering the membrane and damaging it.
• Activated carbon filter: This type of filter specializes in removing chlorine, organic compounds, and other chemical pollutants. Chlorine can significantly damage the reverse osmosis membrane, so an activated carbon prefilter is particularly important to protect the membrane and improve water quality.

Membrane: The reverse osmosis membrane is the heart of the system. It is responsible for the actual filtration and removes even the smallest particles from the water. The membrane works with very small pores, which are able to remove almost all dissolved substances, bacteria, viruses and pollutants. Some reverse osmosis systems even have multiple membranes to increase filtration efficiency.

Post-filter: The secondary filter is arranged after the membrane and has a special function. Although the water is already purified after passing through the membrane, the post-filter gives the so-called osmosis water a fresh taste. This is done by enriching it with minerals, which not only make the water tastier but also healthier. There are different types of post-filters:

• Activated carbon afterfilter: This type of filter provides a final flavor refinement by removing any remaining odors or flavors.
• Mineral afterfilter: These enrich the osmosis water with important minerals such as calcium and magnesium, which were removed during the reverse osmosis process. This not only improves the taste but also increases the health benefits of the water.

Water tank and pressure pump: The water tank is used to store the filtered water. Because the reverse osmosis process is relatively slow, the tank allows constant water removal without having to restart the filter process every time. The pressure pump ensures that there is sufficient water pressure to make the filtration process effective, particularly in households with low water pressure. It increases the pressure on the water so that it is pressed through the dense pores of the membrane and the filtration takes place optimally.

How the reverse osmosis membrane works

Properties of osmosis membrane: The reverse osmosis membrane is made of semi-permeable material that is specifically designed to separate water from almost all dissolved substances. Their structure only allows water molecules to pass through, while retaining larger particles, pollutants, bacteria, viruses, and chemicals.

Pore size and filterability: The pores of the reverse osmosis membrane are extremely small, usually in the range of 0.0001 microns. These tiny pores make it possible to remove even dissolved salts, heavy metals, microorganisms and other contaminants from the water. The filtering capacity is so high that reverse osmosis is one of the most effective water filtration technologies.

The solution-diffusion model: The function of the reverse osmosis membrane is based on the so-called solution-diffusion model. This involves forcing the water through the membrane under high pressure. The membrane does not differentiate directly by the size of the molecules, but by their ability to dissolve in the membrane structure and diffuse through it. Water molecules are able to move across the membrane while leaving larger or undissolved particles behind. This process enables almost complete removal of impurities and dissolved substances in the water, which makes purified osmosis water so special.

One-stage and two-stage process of reverse osmosis

Depending on the desired degree of purity and the application, reverse osmosis can be carried out in a single-stage or two-stage process.

The single-stage process: Basics and Applications

In the single-stage process, the water to be treated flows through a single RO membrane. Here, the water is divided into two streams:

1. Permeate: The purified water that has passed through the membrane.
2. Concentrate: The water that is enriched with retained foreign substances.

Part of the concentrate is fed back into the input side of the plant in the circulating system, while the other part is fed into the waste water. This cycle helps to increase the efficiency of water treatment. However, the membrane must be backwashed at regular intervals to avoid blockage. The permeate is used for purification.

In dentistry, for example, it is common to use reverse osmosis in combination with an ion exchanger to avoid unwanted discoloration due to silica slipping.

One-stage process with EDI (electrodeionization)

In medical applications, the degree of purity of the permeate from a single-stage reverse osmosis system is often insufficient. Therefore, in addition to reverse osmosis, electrodeionization (EDI) is used here. EDI removes ions from the permeate and thus achieves a very high purity of the product water with a conductivity of less than 0.1 µS/cm. A major advantage of this combination is the high yield of product water, while only a small amount of electrode rinse water is produced as waste. The product water can also be fed back into the circuit before the RO membrane. The combination of single-stage reverse osmosis and EDI is particularly used in medical technology, as it effectively prevents discoloration caused by water constituents, such as silica.

The two-stage process: advantages and areas of application

In the two-stage process, two RO membranes are connected one after the other, resulting in a higher degree of permeate purity. Double filtration makes it possible to produce extremely pure product water, which is required in many industrial and medical areas.

Use of two booster pumps

In the standard two-stage process, the water is pressed successively through two membranes. In front of each membrane, there is a pressure booster pump, which operates at a pressure of approximately 12-15 bar. This method is efficient and ensures consistent water quality. The two-stage arrangement increases the purification capacity of the system, which makes it particularly interesting for demanding applications where a very high degree of water purity is required.

Variant with a pump

A rarer variant of the two-stage process works with just one pump, which is installed in front of the first RO membrane. This pump generates a pressure of approximately 30 bar so that there is still enough pressure for the second membrane after the first membrane. Since the first membrane must withstand significantly higher pressure in this case, the system is more technically complex and requires specialized components. However, due to these higher technical requirements, this variant is rarely used.

Osmotic balance and pressure regulation

Osmotic balance and pressure regulation are central aspects of reverse osmosis. An understanding of these aspects is crucial to maximize the efficiency and effectiveness of reverse osmosis systems.

Preventing osmotic balance: Reverse osmosis creates an osmotic equilibrium when the concentration of solutes on both sides of the membrane is balanced. As a result, the water flow stops and the separation becomes inefficient. To prevent this, a constant pressure must be exerted on the membrane that is greater than the osmotic pressure of the solution. This reverses the natural osmosis process and makes it possible to purify the water. Regular monitoring of pressure is therefore crucial to operate the system efficiently.

Use of pressure regulators and pressure exchangers: Pressure regulators are important to keep pressure at a constant level. In reverse osmosis, high pressure is required to overcome the osmotic pressure of the concentrated solution. Pressure regulators ensure that this high pressure remains constant and acts optimally on the membrane. Pressure exchangers are devices that recover pressure from the derived concentrate and feed it back into the system. This increases energy efficiency because less additional energy has to be used to generate the necessary operating pressure. This recovery process is particularly important in large-scale industrial reverse osmosis plants, as it can significantly reduce operating costs.

Energy efficiency and operating costs: Energy consumption is one of the main factors that influence the operating costs of reverse osmosis. By using pressure exchangers, efficiency can be increased and energy consumption reduced by up to 60%. High-quality membranes and efficient pressure regulators also minimize energy consumption by optimising the required operating pressure and reducing component wear. A well-maintained reverse osmosis system runs more efficiently and results in lower maintenance costs. In order to keep operating costs within limits, you should therefore rely on modern pressure exchangers and regulators and carry out regular maintenance work.

Reverse osmosis systems: types, installation, maintenance and practical applications

Different types of reverse osmosis systems

Household investments: These systems are available in various versions:

1. Undercounter reverse osmosis systems: They are installed under the sink and supply the faucet directly. These devices often include a storage tank that stores the filtered water and makes it available when needed. They are ideal for households that require larger amounts of drinking water every day.
2. Tabletop appliances: These devices are compact and easy to set up on the work surface. They do not require a fixed water connection and can therefore be used flexibly, ideal for rental apartments or small kitchens.
3. Tankless systems: Modern, compact systems that work without a storage tank. They use direct filtration and save space.

Industrial plants: In the industrial sector, plant engineering plays a central role in the design and construction of large-scale reverse osmosis systems that are tailored to the specific requirements of the respective sector. Industrial plants are tailored to specific requirements:

1. Drinking water treatment plants: Used in urban or rural supply networks to make tap water safe to drink.
2. Pharmaceutical plants: Produce high-purity water for medical and pharmaceutical purposes, such as in laboratories or in drug manufacturing.
3. Seawater desalination plants: Special systems that can also remove high salinity in seawater. They are robustly built to withstand extreme conditions, for example on ships or in coastal regions.
4. Food and beverage industry: Facilities in this area must comply with the strict hygiene and quality standards of food production. They are used in breweries, beverage bottling plants and large kitchens.

Mobile reverse osmosis systems: These systems are designed for both private and commercial use. Typical designs include:

1. Camping and outdoor systems: Compact, manually operated systems that can be transported in bottles or canisters.
2. Disaster Relief Systems: More robust mobile systems that are used during natural disasters or in crisis areas to quickly provide clean drinking water.
3. Laboratory and research facilities: Mobile reverse osmosis systems in mobile laboratories are adapted for use in changing environments and yet offer high degrees of purity.

Installation: step-by-step guide

1. Preparation: Check the installation site for sufficient space and access to water pipes. Have all the tools you need (screwdriver, pliers, Teflon tape) ready.
2. Switch off the water supply: Turn off the cold water supply system angle valve.
3. Assembly of the tee: Connect the tee to the cold water pipe. Connect the water supply to the reverse osmosis system.
4. Installing the water filter: Secure the pre-filter unit (sediment and activated carbon filter). They are often delivered in separate housings that must be connected correctly.
5. Membrane installation: Open the membrane housing, carefully insert the reverse osmosis membrane and close the housing again.
6. Connect the storage tank: If your system contains a storage tank, connect it to the filter system. Make sure that all tubes are tight.
7. Installing the faucet: If necessary, drill a hole in the sink or countertop and install the included faucet.
8. Sewage pipe: Connect the sewer hose to the drain. If necessary, drill a hole in the drain pipe and secure the sewer hose with a bracket.
9. Flush system: Open the water supply, flush the system, and check that all connections are tight. It may take a few hours before the water is drinkable, as the system must first be cleaned.

Comprehensive documentation of the installation process is helpful to facilitate subsequent maintenance work and possible adjustments to the system.

Maintenance and care

Regular maintenance work should be coordinated through structured project management to minimize plant downtime and ensure efficient operation.

Replacing filters

1. Sediment and activated carbon filters: Replace filters every 6 to 12 months to ensure that the membrane remains protected and works effectively.
2. Reverse osmosis membrane: With optimal care, this lasts around 2 to 5 years. An earlier replacement is necessary if the water flow decreases significantly or the water quality deteriorates.

Membrane cleaning

Thorough chemical cleaning of the membrane is necessary if biofouling or contamination occurs. Use special cleaning solutions to remove deposits such as iron, lime, and organic matter.

Pre-treatment of input water (feed)

1. Mechanical pre-filtering: Use sediment filters (5 microns or finer) to remove particles such as sand, rust, and sludge. This protects the membrane from physical damage.
2. Chemical pretreatment: Use activated carbon filters to remove chlorine and other chemicals as they can damage the membrane. If the water has high degrees of hardness, it is recommended to add descaling agents.
3. Biological pollution prevention: Use UV lamps or dose disinfectants (such as chlorine dioxide) in the pretreatment process to prevent the growth of microorganisms.

Preventing crystallization (scaling) in the membranes

1. Anti-pasting agent: Add special antiscalants to the input water to prevent calcium and mineral deposits from forming on the membrane.
2. Chemical cleaning processes: Do regular chemical cleaning with weak acid or base solutions to remove existing deposits and regenerate the membrane.

Backwashing and preventing membrane blockage

1. Need for backwashing: Backwashing is necessary to remove accumulated particles and microorganisms from the membrane surface and prevent blockages.
2. Monitoring pressure differences: Install pressure gauges before and after the membrane. An increasing pressure difference indicates contamination and signals the need for backwashing or cleaning.
3. Using permeate for backwashing: Use the purified permeate to rinse the membrane and thus remove contaminants. This prevents unwanted substances from reaching the membrane again.

Troubleshoot issues

1. Low water flow: Check the condition of the filters and membrane. A clogged filter or membrane can significantly reduce water flow.
2. Bad taste of water: Check the activated carbon filter. An outdated or saturated filter can no longer effectively remove the flavors.
3. Leaks: Check all connections and hoses. Tighten screw caps and replace leaking seals.

Tips for choosing the right reverse osmosis system

Professional consulting can help you select the right reverse osmosis system.

Important purchase criteria:

1. Capacity and performance: Choose a system with a capacity that meets your daily needs. Household appliances often have an output of between 50 and 200 gallons per day (GPD).
2. Membrane quality: Use high-quality TFC (thin film composite) membranes for a high retention rate (99% or more).
3. Additional filter stages: Multi-stage systems (e.g. 5 to 7-stage) provide comprehensive water purification, including UV disinfection and mineralization.

Well-known manufacturers and brands:

Aquaphor, BestWater, Osmotech, Bluefilters, Waterdrop and Brita are well-known manufacturers. Compare warranties, customer reviews, and available spare parts.

Reverse osmosis in everyday life: practical applications

1. Drinking water for the home: Reverse osmosis water is ideal for drinking, cooking and preparing baby food. It offers a high degree of purity and is free from pollutants such as pesticides, lead and microplastics.
2. Reverse osmosis for the garden: The use of reverse osmosis water is particularly suitable for sensitive plant species such as orchids or bonsais, as they rely on low-lime water.
3. Use for pets: Pets, especially fish in aquariums, benefit from lime-free and pollution-free water. Reverse osmosis reduces water hardness and improves animals' living conditions.
4. Special requirements in dentistry: Dental equipment requires sterile water to minimize infection risks. Reverse osmosis systems produce germ-free water that is used directly for dental units and sterilization devices.

Applications of reverse osmosis

drinking water treatment

Reverse osmosis plays a central role in drinking water treatment, both for private households and for mobile applications. Water treatment plants use reverse osmosis as an intermediate step to remove contaminants, microbes, minerals, and other foreign substances. Various membranes and filters are used, which, in combination with activated carbon and ultraviolet light, ensure that the water is purified.

Mobile reverse osmosis systems offer a practical solution for households in rural areas without access to clean tap water. These systems require a minimum line pressure of around 280 kPa. Even on the high seas and in regions with contaminated tap water, reverse osmosis enables the production of safe drinking water. In some countries, such as when producing mineral water bottles, reverse osmosis is used to remove microorganisms. However, such an approach is not permitted in the EU.

Industrial Applications of Reverse Osmosis

Pharmaceutical industry

In the pharmaceutical industry, pure and ultrapure water is crucial for the production of medicines, solutions and purification systems. Reverse osmosis is used here as a pretreatment step to control water quality. The following aspects must be considered:

• Ultrapure water production: Reverse osmosis removes dissolved ions, organic substances, microorganisms and particles in pharmaceutical water treatment. It thus ensures that the water meets the high standards required for the production of drugs and injection solutions.
• Cleaning of production plants: Ultrapure water from reverse osmosis systems is also used to clean and sterilize production plants. In this sector, it is essential that no residues of cleaning agents, microbes or minerals remain on the surfaces.

food and beverage industry

Reverse osmosis has a wide range of uses in the food and beverage industry, in particular for concentration, filtration and purification. Here are some of the key applications:

• Concentration of liquids: Reverse osmosis is used to concentrate juices, milk and other liquid products. Unlike thermal processes such as evaporation, reverse osmosis works at low temperatures, which preserves product quality, taste and nutritional composition. In the production of fruit juice concentrates, for example, reverse osmosis reduces the water content without destroying the sensitive aromas and vitamins.
• Desalination and mineral removal: In the beverage industry, water quality is crucial. To ensure taste and quality standards, reverse osmosis is used to remove dissolved minerals and salts from water. This is particularly important when producing beverages such as soft drinks, beer or mineral-poor water.
• Manufacture of soft drinks: When making non-alcoholic beer, reverse osmosis is used to remove alcohol from the finished beer. The membranes allow alcohol to pass through while retaining larger molecules such as aromas and flavors. This process makes it possible to largely preserve the original taste.
• Dairy and dairy products: Reverse osmosis is also used in the dairy industry to concentrate milk and whey. The process makes it possible to remove water and concentrate proteins, fats and other valuable components, making further processing more efficient.

Industrial water treatment for technical processes

The use of high-purity water is essential in many industrial processes, particularly when it is used as process water in machines and technical systems.

• Power plants and boiler plants: Reverse osmosis is used in power plants to treat boiler feed water. Boiler water must be virtually free of minerals to prevent calcification, deposits and corrosion in the steam boiler. Reverse osmosis effectively removes lime, salts, and other minerals.
• Cooling water treatment: In technical processes that work with closed cooling systems, the purity of the cooling water is of great importance. Contaminated water can lead to corrosion, deposits and biological growth in the cooling circuits. Reverse osmosis serves as a decisive purification stage here to ensure trouble-free operation of the systems.
• Surface and electroplating industry: In surface technology, reverse osmosis is used to treat water for cleaning, rinsing and electroplating baths. These must be extremely clean to guarantee a high-quality end product. Reverse osmosis removes dissolved substances and thus prevents contamination on the treated surfaces.

Winemaking

Reverse osmosis is used in viticulture to concentrate on must. This process makes it possible to thicken the must — i.e. the juice of the grapes — by removing excess water. This has the following benefits:

• Concentration of all ingredients: The concentration increases the sugar content and flavor intensity of the must, resulting in a fuller, stronger wine. This preserves the aromas and other qualitative characteristics of the grapes, as the process requires no heat.
• Acid and alcohol regulation: In some cases, reverse osmosis is also used to regulate the acidity and alcohol content in wine. During alcohol reduction, the wine mixture is passed through the reverse osmosis system several times to remove only the desired percentage of alcohol.

This method is particularly popular in regions with high rainfall or less ideal growing conditions for grapes in order to produce top-quality wine from average grape material.

Medical technology

Hospital and dialysis applications

In medical technology, reverse osmosis is an important step in the production of ultrapure water, which is used in dialysis, for example. This water must be free from any foreign substances, as it comes into direct contact with the patient's blood during treatment. Medical devices and utensils such as surgical equipment are also cleaned with ultrapure water to eliminate the risk of bacterial contamination.

Special requirements in dentistry

Ultrapure water is also required to clean and disinfect dental instruments to prevent contamination with germs and foreign substances.

Military and space

Water treatment in field camps

The military uses mobile reverse osmosis systems (ROWPU) in field camps to obtain drinking water from almost any water source. These systems can be installed in containers, trailers or stand-alone vehicles. The water is first coagulated, filtered and goes through several reverse osmosis stages before it is finally chlorinated to kill germs.

Reverse osmosis in space stations

Reverse osmosis processes have been developed for NASA to enable stays in space. Even urine is processed and reused as drinking water, which is essential for long-term space missions.

Seawater desalination

Reverse osmosis-based seawater desalination is a complex process in which the water passes through pre-filters and flocculation stages. The addition of acids and anti-coating agents prevents the crystallization of salts, and the use of biocides protects the membranes from biofilms. After reverse osmosis, due to its lack of ions, the water is remineralized before being fed into the drinking water system in order to improve taste and health aspects.

Emergency and mobile water treatment

Mobile reverse osmosis systems are essential in emergencies and disaster areas. They enable the rapid treatment of drinking water from unsafe sources and are compact enough to be transported to various environments as needed.

More uses

Use in aquariums

For aquarists, osmosis water is the ideal basis for the correct water values in the aquarium due to its purity. Due to its neutrality, it can easily be influenced in the desired direction in order to regulate the pH value, which is much more difficult with normal tap water. Osmosis water is particularly beneficial for saltwater aquariums, as it is ideal to enrich with salt. In aquarium technology, reverse osmosis systems are usually preceded by a fine filter and an activated carbon filter to remove dirt and chlorine.

Reverse osmosis for the garden

Reverse osmosis can also be used to obtain particularly soft water for the garden. Plants that rely on low-lime water benefit from the high purity of the water obtained through reverse osmosis.

Advantages and Disadvantages of Reverse Osmosis

Benefits of reverse osmosis

1. Effective removal of pollutants: Reverse osmosis is one of the most effective ways to purify water. It removes up to 99% of pollutants dissolved in water, such as bacteria, viruses, pesticides, heavy metals and chemicals. The tiny pores of the membrane only allow water molecules to pass through and reliably filter out unwanted substances.
2. Improved taste and quality of water: By removing chlorine, lime and other contaminants, the taste of the water is significantly improved. Water that has been purified by reverse osmosis is more neutral and free from unpleasant odors or flavors.
3. Universal applicability: Reverse osmosis systems can be used in a variety of environments, including homes, offices, restaurants, and industrial businesses. They are also suitable for the treatment of brackish water and salt water, which is particularly beneficial in regions with limited freshwater resources.

Disadvantages and challenges of reverse osmosis

1. Water consumption and waste water production: Reverse osmosis is relatively inefficient in terms of water consumption. The production of one liter of filtered water can generate up to three to ten liters of waste water, depending on the efficiency of the plant. This waste water is often drained into sewers or into natural bodies of water such as rivers or the sea. In water-scarce regions, this increased water consumption can put an additional burden on the water supply system and have negative ecological consequences.
2. Purchase and maintenance costs: Reverse osmosis systems are more expensive to buy and install than other water filter methods. In addition, they require regular maintenance, including replacement of filters and membrane. This causes running costs that should not be underestimated. Depending on water quality and intensity of use, filters may need to be cleaned or replaced regularly.
3. Removing essential minerals from water: While reverse osmosis removes many pollutants from water, it also filters out essential minerals such as calcium, magnesium, and potassium. However, these minerals are important for your health. If you only drink reverse osmosis water, this can lead to mineral deficiencies in the long term. Although there are retrofit solutions such as mineralization filters, these involve additional costs and maintenance costs.
4. Potential environmental effects: The production and disposal of the membranes and filter cartridges used can have negative effects on the environment. Many reverse osmosis membranes are made of plastic, which is difficult to recycle. In addition, increased water consumption in areas with water shortages is contributing to an aggravation of water scarcity. The widespread use of reverse osmosis systems in water-scarce cities such as New Delhi can further worsen the already tight water supply situation.

Comparison with other water treatment methods

Compared to other water treatment methods, reverse osmosis has several significant advantages and disadvantages. Here is a comprehensive comparison of reverse osmosis with activated carbon filters, UV disinfection, distillation, and ion exchange.

Activated carbon filter

Activated carbon filters use porous carbon blocks to remove organic matter, chlorine, pesticides, odors, and some heavy metals from water.

• Advantages:
  • Effective at removing chlorine, organic compounds, and certain pesticides
  • Improves the taste and smell of water
  • Affordable and easy to maintain.
• Disadvantages:
  • Does not remove dissolved salts, heavy metals or microorganisms.
  • Must be replaced regularly to ensure effectiveness
  • Not suitable for removing viruses and bacteria.

Compared to reverse osmosis, which removes a wider range of contaminants, activated carbon filters are less comprehensive. While activated charcoal improves the taste and smell of water, reverse osmosis provides more thorough purification.

UV disinfection

UV disinfection uses ultraviolet light to kill microorganisms such as bacteria, viruses, and protozoa in water.

• Advantages:
  • Effective against a wide range of pathogens.
  • No chemicals required, so no effect on the taste of the water.
  • Quick and easy disinfection method
• Disadvantages:
  • Does not remove dissolved salts, chemicals, or heavy metals.
  • The effectiveness depends on the water quality; turbid substances in the water can affect UV radiation.
  • Requires power to the UV light source

In contrast to reverse osmosis, which removes both biological and chemical contaminants, UV disinfection focuses exclusively on eliminating microorganisms. It is therefore suitable as a supplement but not as the sole processing method.

Distillation

Distillation heats water until it evaporates and then condenses it back into liquid. This leaves most contaminants behind.

• Advantages:
  • Removes almost all contaminants, including bacteria, viruses, heavy metals, and dissolved salts.
  • Produces very pure water
• Disadvantages:
  • Very energy intensive and time-consuming.
  • It also removes beneficial minerals from water.
  • The treated water may have a flat taste.

While both reverse osmosis and distillation achieve a very high level of water purity, reverse osmosis is more energy efficient and faster. However, both methods also remove healthy minerals, which is why remineralizing the water is recommended.

Ion exchange

Ion exchange removes ions (e.g. calcium, magnesium) from water by replacing them with other ions (usually sodium or hydrogen).

• Advantages:
  • Effective for softening water (removing calcium and magnesium).
  • Suitable for removing certain radioactive substances.
• Disadvantages:
  • Does not remove organic compounds, microorganisms, or dissolved salts
  • Must be regenerated regularly, often with saline solution.
  • Can increase sodium levels in water, which is not ideal for all people.

Compared to reverse osmosis, which removes a wide range of contaminants, ion exchange specializes in removing specific ions. Reverse osmosis is the more versatile method for comprehensive water purification.

Summary of strengths compared to other water treatment methods

• Removes a wide range of contaminants, including dissolved salts, heavy metals, chemicals, bacteria, and viruses
• Improves the taste and quality of water
• Compared to other methods such as UV disinfection or activated carbon filters, it is one of the most comprehensive water treatment methods.

Common misconceptions and myths about reverse osmosis

There are many misconceptions about reverse osmosis. These myths often lead people to not fully understand the benefits of reverse osmosis water filtering. In the following, we address some of the most common misconceptions.

“Reverse osmosis water is unhealthy”

A common misconception is that reverse osmosis water is supposedly unhealthy because it removes almost all minerals from the water. That's true, but it doesn't mean that it makes the water harmful. The minerals that are removed from drinking water by reverse osmosis are usually present in very small amounts. Our body receives the necessary minerals and nutrients primarily from food, not from drinking water. In fact, reverse osmosis water is particularly pure and free from pollutants, chemicals and microorganisms that can be potentially harmful to health.

If you are still concerned about the mineral content in the water, you can add minerals back to the filtered water. Many reverse osmosis systems offer the option of recycling essential minerals such as calcium and magnesium using remineralization cartridges.

“Reverse osmosis is unnecessary in countries with clean drinking water”

Even in countries with high drinking water standards, there is always contamination in tap water. Although tap water is strictly controlled, substances such as lead, drug residues, pesticides or microplastics may be present in small quantities. The water pipes in the house or apartment can also be an additional source of contamination.

With a reverse osmosis system, you ensure that almost all unwanted substances, including those that are not captured by conventional water filters, are removed from the water. This gives you particularly pure and safe drinking water — regardless of the groundwater quality in your country.

“Reverse osmosis water is the same as distilled water”

Many people equate reverse osmosis water with distilled water, but this is a misconception. Although both types of water are very pure, the difference lies in the type of filtering. Reverse osmosis water is filtered through a semi-permeable membrane that removes pollutants and minerals. Distilled water, on the other hand, is obtained by evaporation and subsequent condensation, which removes all substances, including some volatile compounds.

In addition, reverse osmosis water usually still contains a minimal amount of dissolved substances, while distilled water is almost completely “empty”. While distilled water is mainly used in laboratories and technical applications, reverse osmosis water is ideal for daily consumption.

FAQ — Frequently asked questions about reverse osmosis

How often do reverse osmosis system filters have to be changed?

The filters should be changed regularly to ensure optimum performance of the reverse osmosis system. On average, the following change interval is recommended:

• Pre-filter (sediment and activated carbon filter): every 6-12 months
• Reverse osmosis membrane: every 2-3 years
• Afterfilter (activated carbon): every 12 months

The exact frequency depends on the water quality and the use of the system. Check the condition of the filters regularly and follow the manufacturer's recommendations.

How much water is wasted during reverse osmosis?

Reverse osmosis systems use more water than they produce filtered water. As a rule, about 3-6 liters of waste water are produced per liter of filtered water. The exact consumption varies depending on the model and efficiency of the system. Some modern reverse osmosis systems have water-saving features that can reduce the percentage of wastewater.

Do reverse osmosis water filter systems generate waste water?

Yes, reverse osmosis systems generate waste water. Filtration flushes impurities and excess minerals down the drain. This waste water is referred to as concentrate. Depending on the plant, the wastewater ratio can be between 3:1 and 6:1. However, it is possible in certain cases to use the waste water for other purposes, such as irrigation.

What contaminants does reverse osmosis remove?

Reverse osmosis is one of the most effective ways to purify water. It removes:

• Heavy metals (e.g. lead, mercury, arsenic)
• Chemicals (e.g. chlorine, fluoride)
• Bacteria and viruses
• Pesticides and herbicides
• Salts and dissolved solids (TDS)

This gives you clean and safe drinking water.

Doesn't reverse osmosis also remove the minerals?

Yes, reverse osmosis not only removes pollutants, but also a large part of the minerals contained in water, such as calcium, magnesium and potassium. The purified water is therefore almost mineral-free. Some people appreciate this, while others see the lack of minerals as a disadvantage.

Can reverse osmosis water be treated to add minerals?

Yes, reverse osmosis water can be enriched with minerals later on. There are remineralization filters for this purpose, which are installed after the reverse osmosis system. These add important minerals such as calcium and magnesium back to the water to achieve a balanced taste and mineral content.

What is the difference between an osmosis system and a water filter?

The main difference lies in filtration technology:

• Reverse osmosis system: Uses semi-permeable membranes to filter water under pressure Removes up to 99% of contaminants, including dissolved salts, heavy metals, and microorganisms.
• Water filter: Uses materials such as activated carbon or ceramic to reduce certain contaminants. They are less effective at removing dissolved salts and some chemicals.

Reverse osmosis systems therefore offer more comprehensive purification, but are also more complex and expensive than conventional water filters.

What does osmosis water taste like?

Osmosis water has a neutral, clear taste as it is almost free of impurities and minerals. Some people find it “soft,” while others perceive the taste as “empty” or “flat.” If the taste is too neutral for you, a remineralization filter can help.

Why does the sausage burst during cooking?

During cooking, the sausage absorbs water by osmosis, which increases the internal pressure. At the same time, the outer layers contract due to the heat. If the pressure becomes too high and the sausage casing is no longer flexible enough, it will burst open. To avoid this, you can pierce the sausage before cooking, add salt to the cooking water or cook slowly at a low temperature.

How does osmosis work in plants for the water supply?

Plants use natural osmosis to absorb water from the soil. The roots have a higher solute concentration than the surrounding soil. Water flows into the cells through the semipermeable membrane of the roots to balance the concentration gradient. In this way, the plant supplies its cells with water and nutrients.