Reverse Osmosis Water Filter


The most efficient and timeless water treatment systems are based on reverse osmosis technology.

How a reverse osmosis water filter works


What is reverse osmosis?

The use of reverse osmosis technology lies in the fact that from a more concentrated solution, which is water with organic and inorganic substances dissolved in it, when passing through a semi-permeable membrane into a less concentrated one under the influence of very high pressure, only water molecules pass due to the small size of the pores.

For impurities, the membrane serves as an insurmountable barrier.


Reverse osmosis membranes are made from a composite polymer of uneven density, consisting of two layers, inextricably linked. The outer barrier layer is about 0.00001 inches thick. It sits on a less dense 0.005 inch thick filter layer that is riddled with an incredible amount of micropores.

After reverse osmosis systems, the indicator of dry residue and minerals is determined at a level of less than 6-7 mg / l, in terms of quality, such water is close to melted or glacial.

In domestic and semi-industrial reverse osmosis systems, roll filter elements are used.

In this design, the semi-permeable membrane is enclosed in a flask with an inlet and outlet for connection to a water supply system, and is a rolled-up polymer film consisting of two layers: water-collecting and water-supplying.

The plant is supplied with source water under high pressure, which, being filtered, forms permeate (filtrate) and concentrate (impurities).

The permeate collects on the catchment layer of the membrane and spirals down into the central tube. The concentrate accumulates from the other end and then drains into the drain.

Types of membranes that are used:

  • Ultrafiltration – pore size – 0.1-0.002 microns. Capable of retaining colloidal suspensions, bacteria and viruses.
  • Nanofiltration – pore size – 0.002-0.001 microns, retain suspended and dissolved impurities, including nitrates, nitrites and salts of heavy metals. The difference is the ability to pass dissolved minerals.
  • Reverse osmosis – pore size less than 0.0001 microns, which corresponds to the size of a water molecule. This means that substances that are present in the form of suspensions or solutions are retained on the membrane. Reverse osmosis technology is successfully used in medicine and pharmaceuticals. When preparing for drinking purposes, additional processing on mineralizers is required.

Important! Depending on the type of membrane used in filtration systems, you should focus on the number of purification steps and the quality of the source water! The pore size of the membrane is directly proportional to the resistance to flow: the smaller the pores, respectively, the greater the pressure required for the filtration process.

Characteristics of reverse osmosis water filters


The reverse osmosis filter is connected to the water supply, from where the source water is supplied to the installation, and the concentrate obtained after cleaning is discharged into the sewerage system. Unlike other models, membrane units are connected at the point where potable water is required. As a rule, this is a kitchen with a separate tap equipment.

The quality of purified water, its quantity and the operating conditions of the reverse osmosis system depend on the following conditions:

  • Pressure. For operating performance, the pressure in the system must be at least 2.8 atm.
  • Temperature. For normal operation, the water temperature should be between +4 and +35 degrees Celsius.
  • The quality of the source water. The performance and service life of the membrane depends on the initial contamination. With some types of pollution, the performance can be increased by increasing the operating pressure. High levels of dry residue, bicarbonate hardness, calcium and magnesium salts lead to premature membrane fouling, and its regeneration is more often required.

Installation performance is measured in gallons (GPD). Household filters can have the following parameters:

  • 36 GPD, which equals 132 l / day;
  • 45 GPD, which equals 170 l / day;
  • 50 GPD, which equals 189 l / day;
  • 75 GPD, which equals 283 l / day;
  • 100 GPD, which is equal to 378 l / day.

Actual performance may differ from the declared, the parameter depends on the operating conditions.

A typical membrane installation includes 5 to 7 stages.

Basic equipment:

  • preliminary three-stage cleaning (replaceable cartridges with polypropylene and carbon cartridges);
  • reverse osmosis membrane;
  • final cleaning (charcoal cartridge).

Additionally connected:

  • ultraviolet lamp for biocidal treatment;
  • bioceramic cartridge or mineralizer.

Priority belongs to the pre-cleaning stage, the purpose of which is to ensure the normal operation of the installation. As a rule, three filters are used in series:

  • mechanical polypropylene with a pore diameter of 5 microns. It is designed to extract large particles such as rust, sand and other suspensions;
  • carbon pre-filter. Removes up to 95% of organic pollutants, including oil products, chlorine and organochlorine compounds, including salts of heavy metals, manganese and iron;
  • mechanical polypropylene filter with a pore diameter of 1 micron, retains suspended matter and colloidal substances.

At the next stage of work, the main processing takes place on a reverse osmosis membrane. After that, the permeate enters the carbon filter for final purification. Separately, the reverse osmosis filtration system is supplemented with a UV lamp for bactericidal treatment and special cartridges – mineralizers and structurators.

Their purpose is to enrich purified water with useful minerals and restore its natural physical structure.

The filtered water is fed into a storage tank with a volume that depends on the model and performance. As you use the system automatically adds a portion of purified water to the tank. Storage tanks are made of high quality enamel coated steel sheet.

Inside, using a silicone membrane, the container is divided into two chambers. Air is pumped into the lower one under pressure, due to which, when the water level in the upper chamber decreases, the silicone membrane increases in size and compensates for the pressure in the tank until it is completely drained.

A nipple is installed in the air chamber, with the help of which, if necessary, the level of air pressure in the storage tank is regulated.



In membrane installations, the most expensive replaceable element is a reverse osmosis membrane. The service life is directly affected by the quality of the water supplied for treatment: suspended solids, free chlorine, and hardness salts block the operation. Flushing is carried out to restore working performance.

Regeneration is required if the membrane performance has fallen by 20% relative to the rated power.

The procedure is performed 2-3 times a year using special acidic and alkaline reagents (antiscalants) to remove contaminants.

Acid washing is carried out in the case of inorganic deposits such as calcium and magnesium carbonates, iron and manganese hydroxides.

Washing with an alkaline solution is performed when contaminated with organic substances and colloidal suspensions.

The filter unit is disinfected annually using special disinfectant solutions.

Important! Domestic reverse osmosis systems must not be used to treat microbiologically contaminated water or water of unknown origin! You should carefully monitor the technical parameters of the installation and replace the replaceable elements in time. Otherwise, water quality is not guaranteed!

The main parameter that ensures high-quality and long-term operation of all filter elements, and especially the membrane, is sufficient pressure. At a working pressure of 4-6 atmospheres, the installation runs smoothly.

At a pressure below 3 atmospheres, the life of the membrane element is significantly reduced, and at a pressure below 1.2 atmospheres, filtration stops. If the pressure in the system is less than 2.8 atmospheres, it is recommended to install a pump.

When operating reverse osmosis plants in conditions of water supply with increased hardness, it is advisable to install softeners – filters with ion-exchange loads at the pre-treatment stage.

Pros and cons of reverse osmosis filters


Manufacturers of membrane plants offer the widest range of products to meet any need.

What should you pay attention to when choosing?

  • The number of degrees of purification. In the basic configuration, all filters have at least 5 stages of purification, which ensure the standard water quality, subject to the operating rules. Additional modules are installed at the request of the client.
  • The quality of plastic for the manufacture of filter housings. This parameter is important, as the housing of the modules must withstand high pressure, not impart a “chemical smell and taste” and not have pores on the inner walls so that microorganisms do not accumulate in them. When using low-quality raw materials, the module cases crack, which can result in a flood.
  • The quality of fittings and connections. No less important point than the previous one. Since the system operates under conditions of constant high pressure, about 4-5 atmospheres, it is important that it is equipped with high-quality connections, fittings and main piping units.
  • Membrane quality. This is the “heart” of the filtration plant, and not only the normal operation of all units depends on it, but also the quality of the treated water, which is then used for drinking.
  • Crane for pouring. This is the element of the filter, which is always in sight. For aesthetic reasons, it is better to choose it in accordance with the interior of the kitchen.



In case of insufficient pressure and incorrect operation of the filtration unit, the following problems may occur:

  • Reducing the operational resource;
  • Premature contamination of pre-filters;
  • Incomplete filling of the storage tank;
  • Insufficient amount of water in the storage tank;
  • Lack of water delivery when the storage tank is full;
  • Increasing the amount of drainage water;
  • Accelerated silting of filter housings;
  • Change in the taste of water and the appearance of scale when it is boiled;
  • Problems with turning the pump on or off;
  • Extraneous sounds during pump operation;
  • Overheating of the power supply;
  • Non-stop discharge into the sewer;
  • Increasing the flow rate on the meter compared to the normal mode.

If the cleaning system does not work properly, you should notify the maintenance service and do not correct the breakdown yourself. The working life of the cartridges is calculated on average for six months of uninterrupted operation.

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