Replacing filters in a reverse osmosis system: when, how and which ones to choose

A reverse osmosis system is not just a water filter, but a complex complex that requires regular maintenance. Many owners install such systems to get crystal clear water, but forget about the need to timely replace cartridges. As a result, the water quality gradually deteriorates, and the reverse osmosis membrane fails prematurely.

If you notice that the water from the tap has become cloudy, acquired an unpleasant taste or smell, and the pressure has decreased, these are sure signs that it is time to change the filters. But how often should this be done? Which cartridges should I choose for replacement? And is it possible to cope with the task on your own, without resorting to the help of specialists? In this article we will go through everything step by step - from theory to practice.

Why is it important to change filters in a reverse osmosis system on time?

The main task of a reverse osmosis system is to remove 98-99% impurities, including heavy metal salts, chlorine, bacteria, viruses and even some types of medications. However, over time, the filter elements become clogged with contaminants and cease to cope with their function. This is what happens if you ignore the replacement:

• 🦠 Bacteria reproduction: The moist environment inside a clogged filter becomes an ideal environment for the growth of microorganisms. Instead of purification, the water may become enriched with harmful microbes.
• 🧂 Deterioration of taste: Old carbon filters begin to release previously absorbed substances back, giving the water an unpleasant taste.
• 💧 Decreased performance: The reverse osmosis membrane operates under pressure, and if the pre-filters do not purify the water properly, it will quickly clog.
• 💰 Additional costs: Ignoring the replacement of filters leads to breakdown of the membrane (the cost of which is 3-5 times higher than that of standard cartridges) or even the entire equipment.

According to research, If filters are not replaced in a timely manner, the concentration of harmful substances in “purified” water may exceed the norm by 2-3 times. For example, if the carbon filter is not changed for more than a year, it begins to release previously accumulated pesticides and organochlorine compounds into the water.

⚠️ Attention: If your reverse osmosis system is connected to hot water (which is strongly not recommended), the filters will wear out 2-3 times faster due to thermal effects. In this case, replacement must be carried out every 3-4 months.

When to replace filters: when is it time to act?

Manufacturers of reverse osmosis systems always indicate recommended filter replacement times in the instructions. However, these data are average. Actual service life depends on:

• 🏡 Source water quality (hardness, iron content, chlorine, mechanical impurities).
• 💧 Usage intensity (the volume of water passed through the system daily).
• 🌡️ Water temperatures (cold or warm).
• 🔧 System Models (some brands, e.g. Atoll or Barrier, use more durable materials).

Filter type	Average replacement time	Signs of wear
Mechanical filter (5 microns)	3-6 months	Reduced water pressure, visible particles in the glass
Carbon filter (granular or compressed)	6-12 months	Chlorine taste or chemical odor
Fine filter (1 micron)	6-9 months	Cloudy water after prefiltration
Reverse osmosis membrane	2-3 years	Increased amount of drainage water, deterioration of taste
Post-filter (carbon or mineralizer)	12 months	Unpleasant taste or odor in purified water

To accurately determine the replacement period, you can use TDS meter - a device that measures the level of salts in water. If the value of purified water begins to increase (for example, from 10-20 ppm to 50-100 ppm), this is a signal that the membrane or pre-filters require replacement.

Which filters to choose for replacement: overview of types and brands

There are hundreds of reverse osmosis filter models on the market, and choosing the right ones can be difficult. Main rule: Cartridges must match your system model. For example, filters for Atoll A-550m not suitable for Aquaphor OSMO 50 due to different diameters and types of connections.

The main types of filters that will be required for replacement:

• 🔄 Mechanical filters: remove rust, sand, silt. They are made of polypropylene (cheap, but require frequent replacement) or fiberglass (more durable). Popular brands: Pentek, Culligan.
• ☠️ Carbon filters: remove chlorine, organic compounds, pesticides. They can be granulated (cheaper, but less effective) and pressed (for example, Matrikx CTO).
• 🧲 Fine filters: traps particles up to 1 micron in size. Polyethersulfone cartridges are often used (PES).
• 💎 Reverse osmosis membranes: the main element of the system. The best membranes produce Dow Filmtec, Toray, CSM. Service life - 2-3 years with proper prefiltration.
• 🧪 Postfilters: final cleaning and taste improvement. There are coal (GAC) or with mineralization (Aquaphor B510-08).

When choosing, pay attention to:

• 📏 Size: standard - 10" (254 mm) or 20" (508 mm).
• 🔌 Connection type: threaded (1/4", 3/8") or quick-connect.
• 📊 Degree of purification: for membranes - percentage of salt retention (98% and above).

⚠️ Attention: Cheap membranes from unknown brands (eg "no-name" from China) may have salt retention rates below 90%. This means that up to 10% of harmful impurities will remain in your “purified” water. Check quality certificates!

Step-by-step instructions for replacing reverse osmosis filters

Replacing filters is not a complicated process, but it requires care. If you've never done this before, it's best to prepare your tools and study your system's wiring diagram in advance. In most cases, a flathead screwdriver, an adjustable wrench and new cartridges are sufficient.

General replacement algorithm:

1. Disconnect the system from the water supply and drain the remaining water by opening a clean water tap.
2. Close the water tap at the entrance to the system (usually located under the sink).
3. Remove the filter flasks, unscrewing them with a special plastic key (included) or manually.
4. Remove old cartridges and wash the flasks with warm water and soap (no aggressive detergents!).
5. Install new filters, observing the order (usually it is indicated on the flasks: 1st, 2nd, 3rd).
6. Assemble the system, check the tightness of the connections.
7. Flush the system: Turn on the water and drain the first 10-15 liters (they may contain coal dust).

Pay special attention to the reverse osmosis membrane. Replacing it takes more time:

Turn off the water and power to the pump (if equipped)

Remove the membrane housing cover (usually it is secured with clips)

Remove the old membrane and wash the housing

Install the new diaphragm (make sure the O-rings are in place)

Check the tightness after assembly-->

If after replacing the filters the water flows too slowly or too much water goes into the drain, check:

• 🔧 Correct installation of the membrane (it must be tightly fixed).
• 💧 Pressure in the system (the norm is 2.8-4 atm; at low pressure the membrane works worse).
• 🔄 Presence of air in the system (sometimes repeated flushing is required).

What should I do if the water is cloudy after replacing the filters?

This is normal in the first 10-15 minutes - this is how coal dust is washed out of new cartridges. If the cloudiness persists for longer, check:

1. Tightness of connections (possibly air is being sucked in).

2. The quality of new filters (defective cartridges may crumble).

3. System pressure (if the pressure is too high, the membrane may allow particles to pass through).

Common mistakes when replacing filters and how to avoid them

Even experienced users sometimes make mistakes that lead to system breakdown or deterioration in water quality. Here are the most common of them:

• 🔀 The filter order is mixed up. For example, if you put a carbon filter in place of mechanical cleaning, it will quickly clog and fail. Solution: Always check the labeling on the flasks (they are usually numbered).
• 💦 Ignoring system flushing. If you do not drain the first liters of water after replacing, there will be coal dust in the glass. Solution: flush the system for 10-15 minutes.
• 🔧 Excessive tightening of flasks. Plastic housings can crack if too much force is applied. Solution: Tighten by hand until it stops, without tools.
• 🧼 Using detergents to wash flasks. Aggressive chemicals can damage seals. Solution: Wash only with warm water and mild soap.
• ⏳ Replacement of membrane only, without pre-filters. If the prefilters are clogged, the new membrane will quickly fail. Solution: change all filters in a comprehensive manner.

Another typical problem is leak after assembly. Most often it occurs due to:

• Worn o-rings (they need to be changed every 2-3 filter replacements).
• Uneven installation of the membrane (it should lie flat, without distortions).
• Damaged tubes or fittings (check for cracks).

⚠️ Attention: If after replacing the filters the system begins to make loud sounds (hissing, knocking), turn it off immediately! This may be a sign of a membrane rupture or a leak. Check all connections and pressure in the system.

Reverse Osmosis System Maintenance: Additional Tips

Replacing filters is only part of system maintenance. To make it last longer, keep an eye on:

• 💧 Water pressure: If it is below 2.8 atm, the membrane is not working effectively. The solution is to install a booster pump (for example, Aquatech AT-BP15).
• 🌡️ Temperature: the optimal water temperature for the membrane is 10-25°C. Hot water shortens its service life.
• 🔄 By drainage flow: if too much water goes into the sewer (more than 3-4 liters per 1 liter of clean water), the membrane requires replacement.
• 🧼 Cleanliness of the storage tank: Once a year it should be washed with a weak solution of vinegar or citric acid.

If your system is equipped UV lamp (for example, in models Atoll A-580U), do not forget to change it once a year. UV radiation weakens over time and bacteria are no longer destroyed.

For those who want to automate the process, there are systems with replacement indicators (for example, Aquaphor DWM-101S). They are equipped with resource sensors that signal the need to replace filters.

FAQ: Frequently asked questions about replacing reverse osmosis filters

Can old filters be washed and reused?

No, this is absolutely not recommended. Filters (especially carbon and membrane filters) accumulate contaminants that cannot be completely washed out. Flushing may temporarily improve water pressure, but the quality of cleaning will deteriorate. The exception is mechanical filters made of stainless steel (they can be washed with a reverse flow of water).

What happens if you don’t change the reverse osmosis membrane for 5 years?

The membrane degrades over time: its pores increase, and it begins to let salts, bacteria and other impurities through. As a result, “purified” water becomes almost the same as from the tap, but with the addition of accumulated contaminants. In addition, the old membrane may rupture, which will lead to a flood.

How do you know when it's time to change the post filter?

Main features:

• Unpleasant taste or odor in purified water (for example, “chemical” or “plastic”).
• Turbidity of water after a long period of inactivity of the system (more than 2-3 days).
• Deterioration in the taste of tea/coffee prepared with purified water.

It is recommended to change the post-filter once a year, even if there are no signs of wear.

Can I replace the filters myself if the system is under warranty?

Yes, replacing filters does not affect the warranty on the system itself (unless you damage it in the process). However, if the warranty also covers consumables (which is rare), it is better to contact a service center. Always keep receipts for filter purchases - they may be needed for warranty service.

Which filters are better - domestic or imported?

Quality does not depend on the country of origin, but on the brand and technology. Among domestic brands, they have proven themselves well Aquaphor, Barrier, Geyser. Among imported ones - Dow Filmtec (membranes), Pentek (cartridges), Culligan. The main thing is to buy filters from trusted stores, as there are many fakes on the market.