Mechanical water filtration: comparison of 10, 50, and 120 micron cartridges

We are still preparing products.

But you can look at other categories.

Mechanical water filtration: comparison of 10, 50 and 120 microns cartridges

When a customer comes for the first time to address water filtration from a well or their own borehole, they usually ask one specific question: "Which microns should I buy?" At first glance, a simple question – in practice, however, the answer has many layers. Mechanical filtration is not just about catching "some sand". It is about protecting the pump, the lifespan of the entire water supply system, the comfort of water in the household, and about not having to replace membranes, valves and valve seats in a year because you underestimated the coarse pre-filtration.

In this article, we will go through in detail what microns as a unit of filtration actually means, what is the physical difference between the values of 10, 50 and 120 microns, in which situations each size is used, what are the consequences of a wrong choice, and how to assemble a system that will really work for years without unnecessary problems.

What is a micron and why it matters

A micron (μm, micrometer) is one millionth of a meter, that is, one thousandth of a millimeter. For comparison: the diameter of a human hair is about 70 microns. Bacteria range from 0.5 to 10 microns, sand grains are typically 100–500 microns, and coarser river sand even more. When we talk about a filter cartridge with a value of 50 microns, it means that this cartridge will capture solid particles larger than 50 μm – and everything smaller will pass further.

This is the basic principle of mechanical (sediment) filtration: physical capture of solid impurities based on their size. It does not use any chemistry, no ion exchange, no biological processes. Therefore, mechanical filtration is always the first line of defense – it must precede any other water treatment.

The capture capacity is sometimes stated as "nominal" or "absolute". A nominal value means that the filter captures at least 85–95% of particles of a given size. An absolute value guarantees the capture of practically 100% of particles above a certain limit. Most common household cartridges work on the nominal principle – which is fully sufficient for common applications.

Filtration of 120 microns: coarse pre-filtration before the pump

The value of 120 microns is the coarsest filtration class that you commonly encounter in household waterworks and well installations. It captures coarse sand, drilling residues, larger organic fragments, leaves from the well, and other macroscopic impurities. A diameter of 120 μm is still visible to the naked eye as fine dust.

When and where is this class used? Primarily as a suction filter directly before the pump – that is, in the suction pipe between the well and the pump. In this position, the pump has not yet created pressure, the water only flows from its own height or is being sucked in, so the pressure drop on the cartridge is minimal. A coarse cartridge protects the impeller and bearings of the pump from abrasive particles. Every sand particle that passes through the pump mechanically wears out its internal parts – and the repair or replacement of the pump costs many times more than a protective filter.

A typical product for this position is Sand filter 1" 120–130 mcr – for suction before the pump. This filter is specifically designed for suction position: it has low hydraulic resistance, a robust body and a basket (cartridge) made of durable material that can withstand long-term contact with water of various quality. It is important that this type of filter is installed before the pump, not after it – this is a mistake that customers occasionally make and then wonder why the pump is losing performance or has problems with suction.

Practical scenario: a well with a sandy bottom

Imagine a typical dug well in Záhorie or in the Danubian Lowland – typical areas with sandy geology. After every heavy rain or when the pump is sucking too fast, water lifts sand from the bottom. Without a sand filter before the pump, this sand gets directly into the impeller. After two years of operation, the pump starts to make noise, loses maximum pressure and eventually the bearing fails. The customer thinks they had a "bad pump" – but the problem was the lack of protection before the pump. With a 120-micron suction filter, this problem simply does not arise.

50 micron filtration: the universal workhorse for well water

Fifty microns is the most commonly used filtration class for households supplied by their own well or borehole. It captures finer sand, silt particles, rust from pipes, fibers, larger organic particles, and yet does not cause a significant pressure drop or rapid clogging with normally contaminated well water.

In this category, cleanable inserts stand out above all – that is, filters that do not need to be discarded after clogging, but can simply be rinsed under running water or in a container, or blown through with air, and continue working. For the 50-micron class, this is a very practical compromise: the insert clogs slowly enough that replacement is not necessary every two weeks, and at the same time, the filtration is fine enough to protect the installation.

A specific example is the Mechanical insert 10" RL SX 50 mcr cleanable – an SX format insert for Atlas Filtri Senior filters. Its construction consists of a special polypropylene mesh with a defined mesh size of 50 μm, which can be rinsed and reused after clogging. The lifespan of such an insert in standard well water can be 1–3 years, depending on water quality and cleaning frequency.

When is 50 microns the right choice?

Well or borehole with normal sedimentation (sand, silt, rust)
Main filter behind the pump in a single-filter system (MONO assembly)
First stage of a two-filter system (DUO), when the second stage is 10 mcr
Households where water preparation for a UV lamp or reverse osmosis is not required
Garden and utility water supplies, sprayers, filling stations

In practice, I often encounter customers who want to start immediately with 10-micron filtration, thinking that finer is better. This is not true, however. A finer insert clogs much faster, causes a higher pressure drop, and with more heavily contaminated water, it can clog within a few days. For most domestic water systems, 50 microns is the ideal first stage of filtration.

10 micron filtration: fine protection for sensitive applications

Ten microns is a relatively fine class of mechanical filtration. At this level, fine clay and silt particles, larger bacterial clusters (individual bacteria are mostly smaller, but their colonies and slime can be over 10 μm), corrosion residues from pipes, organic fibers, and similar invisible impurities are captured.

10 mcr filtration is almost always the last stage of mechanical filtration before further water treatment or before sensitive appliances. Before a UV lamp, water must be mechanically cleaned to at least 10–20 microns, because turbidity in the water can shadow bacteria from UV radiation and disinfection is not effective. Before reverse osmosis, a 10-micron (or even 5-micron) pre-filter is used to protect the membrane from premature clogging.

For households where well water is also used for drinking (without other treatment, only mechanical filtration), a 10-micron insert significantly improves the organoleptic properties of the water – it will be cleaner, clearer, and free of visible turbidity.

A typical product is the Mechanical insert 10" FA 10 mcr wound, sediment. This is a wound insert – a technology in which fibers (polypropylene or cotton) are wound around a core to form a denser mesh inward. Wound inserts have depth filtration: they capture impurities not only on the surface but also throughout the entire volume of the insert. This gives them a higher capture capacity at finer filtration. The disadvantage is that they cannot be cleaned after clogging – they must be discarded and replaced with a new one.

Practical scenario: water preparation for a UV lamp

A customer has a borehole, and the water analysis shows microbiological contamination (coliforms). They decide on UV disinfection. But a UV lamp alone cannot work effectively if the water is turbid – every turbidity particle reduces the permeability of UV radiation. The solution is to install at least a 10-micron filter before the UV lamp. The water entering the UV chamber must be mechanically clean so that the radiation can penetrate the entire volume. Without this pre-filter, bacteria "hidden" behind the impurities may survive the disinfection.

Types of inserts: wound vs. cleanable – what does it mean in practice

Along with the micron value itself, the construction of the insert is also important. In practice, we encounter two basic types: wound (sometimes marked as FA – fiber, or CTO) and cleanable (mesh, type SX in the Atlas Filtri system).

Wound inserts

Wound inserts are made by winding fiber (polypropylene, cotton, glass fiber) around a perforated core. Filtration is depth-based – impurities are captured not only on the outer surface but also within the material. This means a higher capture capacity for the same external size. Disadvantage: the insert cannot be effectively cleaned. After clogging, it must be completely replaced. Therefore, wound inserts are typical for finer filtrations (10 mcr and below), where they are changed regularly – usually every 3–6 months depending on water quality.

Cleanable mesh inserts (SX)

Cleanable inserts are made of plastic or stainless steel mesh with a precisely defined mesh size. Filtration is surface-based – impurities are captured only on the outer surface of the mesh. The advantage is clear: we remove the insert, rinse it (or blow it through), and put it back in. The disadvantage: the capture capacity is lower than that of a wound insert of the same size, and surface filtration is less effective for very fine particles. Therefore, cleanable inserts are mainly used for coarser filtration – 50, 100, 120 microns.

For more information on choosing between these types, please read the article How to choose the right filter insert: wound vs. cleanable SX insert in our Knowledge Center.

Filter bodies: MONO and DUO, format 10" and connection 1"

The insert itself cannot function without a filter body – we are talking about a filter housing into which the insert is inserted. The 10" format (i.e., a ten-inch insert, length approx. 25 cm) dominates the market. It is a globally standardized format and inserts from different manufacturers are mutually compatible (with some exceptions for SX profile inserts).

MONO filter is a simple assembly with one filtration stage. It is sufficient for less demanding applications – for example, when the well produces relatively clean water and you need only one stage of protection. A typical example is the Filter SENIOR 10" MONO connection 1" – a solid, proven assembly from Atlas Filtri, suitable for standard home installations.

DUO filter combines two filter bodies in sequence within one assembly. It allows the use of a coarser insert (e.g., 50 mcr) in the first stage and a finer one (e.g., 10 mcr) in the second stage, enabling multi-stage filtration in one compact unit. This solution is ideal for water with higher turbidity or where a UV lamp or other technology sensitive to turbidity follows the filtration. Specifically: Atlas Filtri Senior 10" DUO 1" – Double water filter for SX inserts is a professional solution for more demanding households.

For a more detailed discussion of the differences between MONO and DUO assemblies, see the article What filtration is enough for me: MONO vs. DUO filter – differences and when to use which, where you will also find practical examples from real-life applications.

How to assemble the right filtration system: practical combinations

In practice, a filtration system is designed from the water source towards the point of use. The main rule is: always proceed from coarse to fine filtration. Never the other way around. The reason is simple – a fine insert clogged with coarse impurities becomes blocked much faster, and its capacity is wasted unnecessarily.

System for a standard household with a well (medium water quality)

Position 1 – Suction filter before the pump: 120 mcr sediment filter – protects the pump from coarse impurities
Position 2 – Pressure filter after the pump: MONO filter or first stage of DUO with 50 mcr insert – captures remaining fine sand, silt, rust
Position 3 (optional) – Fine filtration: Second stage of DUO with 10 mcr insert – before UV lamp or before drinking water branch

System for garden use (sprinkler, filling station)

Suction filter 120 mcr before the pump – essential base
Filter 50 mcr after the pump – protection of sprinkler nozzles and valves
10 mcr filtration is not necessary – utility water, not drinking water

System for drinking water from a well with microbiological contamination

Suction filter 120 mcr before the pump
Filter 50 mcr after the pump (first stage of DUO)
Filter 10 mcr (second stage of DUO or standalone filter)
UV lamp – only after thorough mechanical pre-filtration

Details on installation and hydraulic connections are described in the article Wall mounting of a water filter step by step: bracket, connection, sealing.

Pressure drop: when a filter harms instead of helping

One of the most common problems we encounter in the field is the neglected replacement or cleaning of the filter insert. A filter works well as long as it is clean. When it starts to clog with impurities, the differential pressure across the insert – the difference in pressure before and after the filter – increases. With significant clogging, the pressure drop can reach 0.5–1.5 bar, which, with a typical household pressure of 2.5–3.5 bar, represents a noticeable drop.

Result: water flows weakly from the farthest tap. The customer assumes the pump is weak or the piping system is inadequate. I arrive, look at the filter, turn the air vent – and black, muddy water comes out of the filter. The insert is clogged and filters only minimally. After replacing the insert, the pressure returns to normal. This is not an exception – this happens regularly, and it is why it is a good practice to install pressure gauges before and after the filter body, or at least visually check the condition of the insert every 2–3 months.

Practical rule: if you have a filter with a 50 mcr passage and the water is usually turbid (slightly discolored after rain), plan to clean the insert every 4–8 weeks. With a 10 mcr insert in the same water, it may happen that you will need to clean it every 2–3 weeks – which is already impractical. The solution is multi-stage filtration: 50 mcr captures most impurities, and the 10 mcr insert clogs much more slowly, as it receives pre-filtered water.

More about solving problems can be found in the article Common water filter problems: leaks, pressure drop, clogged insert.

Filter maintenance: cleaning and replacement intervals for cartridges

For 120-micron sediment filters (mostly washable baskets): visual inspection once a month, cleaning as needed – in a normal well this may be every 3–6 months, in a dirty well even every month.

For 50-micron washable mesh cartridges (SX): cleaning every 4–12 weeks depending on water quality. Remove the cartridge, rinse it under running water from the inside out (not the other way around, to avoid pulling dirt deeper into the mesh), or soak it for 30 minutes in a weak citric acid solution for lime deposits. Replace the cartridge once every 1–3 years or if it loses its shape, cracks, or cannot be cleaned.

For 10-micron wound cartridges: replacement every 3–6 months with regular use. A wound cartridge cannot be rinsed – any attempt to clean it will deform the fibers and the filter will stop working properly. Replacement is simple: unscrew the filter body, remove the old cartridge, insert a new one, and tighten. The whole process takes 5 minutes.

For detailed information on cleaning washable cartridges, see the article Washable well water filter cartridges: how and when to clean and replace them.

Most common mistakes when selecting and using filters

Missing suction filter before the pump: The most common mistake. A pump without protection will fail within a few years.
Too fine a cartridge in the first stage: A 10 mcr cartridge as the only filter in a dirty well will clog within days.
Forgotten cartridge replacement: A neglected cartridge no longer protects but actually harms – it increases pressure drop and can serve as a breeding ground for bacteria.
Filter placed after the pump instead of before: A suction filter (120 mcr with low hydraulic resistance) is a different construction than a pressure filter after the pump.
Wrong connection size: Filters in this category usually have a 1" (inch) connection. If your system is 3/4", you will need a reducing adapter. The article Filter cartridge size 10" and connection 1" – what do these parameters mean? explains what these numbers actually mean.
Ignoring water analysis: Before deciding on the setup, have your water tested. You will not only find out the turbidity, but also the content of manganese, iron, or microbiology – these determine further filtration steps. More on this is covered in the article How to choose a well water filter: what to focus on before buying.

Summary comparison of filtration classes in a table

Parameter	120 microns	50 microns	10 microns
Typical position	Suction filter before the pump	1st stage after the pump	2nd stage, before UV/RO
What it captures	Coarse sand, stones, large fragments	Fine sand, silt, rust, fibers	Fine turbidity, silt particles, bacterial clusters
Cartridge type	Washable (basket/mesh)	Washable mesh (SX)	Wound (disposable)
Pressure drop (clean cartridge)	Minimal	Low	Medium
Cleaning intervals	As needed, washable	4–12 weeks, washable	Replace every 3–6 months
Suitable for	Pump protection	Well water, garden, utility water	Drinking water, before UV lamp, before RO
Average cartridge price	Included in the filter body	Low (long lifespan)	Low (regular replacement)

Frequently asked questions (FAQ)

Can I use only one 10 mcr filter instead of a multi-stage setup?

Technically yes, but in practice it is a bad idea. If the well water contains a normal amount of sand and silt, a 10-micron cartridge will clog very quickly – sometimes within a few days. The result is frequent cartridge replacements, high costs, and constant work with the filter. The correct solution is to pre-filter with a 50 mcr cartridge, which captures most of the coarse impurities, and the 10 mcr cartridge then works only with pre-cleaned water – its lifespan is extended many times over. And don't forget the 120 mcr suction filter before the pump – it protects the pump itself.

Can filters be installed in any order?

No. The order is essential. A coarser filter must always be placed before a finer one. If you were to place a 10 mcr cartridge before a 50 mcr cartridge, the fine cartridge would clog very quickly (it captures all the coarse impurities, which it is not designed for), while the coarse cartridge would do nothing meaningful. The correct order: 120 mcr (suction) → pump → 50 mcr → 10 mcr → UV/RO → consumption.

Is 10 mcr filtration sufficient for drinking water?

For mechanical cleaning, yes – the water will be visually clean and free of visible turbidity. But mechanical filtration alone does not remove bacteria, viruses, heavy metals, or chemical contamination. If the well water is microbiologically contaminated, it is necessary to add UV disinfection, chlorination, or reverse osmosis. 10-micron filtration is a necessary condition for the effectiveness of a UV lamp, not a guarantee of drinking water safety.

How do I know it is time to replace or clean the filter cartridge?

The most reliable indicators: noticeable pressure drop in the house, weak water flow from taps, visible turbidity or color in the water. Ideally, you should have pressure gauges before and after the filter – if the pressure difference is more than 0.3–0.5 bar from normal, it is time to act. For 10 mcr wound cartridges, we recommend planned replacement every 3 months, regardless of visual condition – the cartridge may be clogged inside, even if it does not look bad from the outside.

Are SX inserts from Atlas Filtri compatible with other filter bodies?

SX format inserts (used in the Atlas Filtri Senior and Duo series) have a special gripping profile at the top end, which is not the standard 10" size. They are primarily designed for Atlas Filtri Senior bodies. Standard 10" wound inserts (FA, PP) are generally more compatible and fit into most 10" bodies from various manufacturers. Always verify the compatibility of the insert with your filter body before purchasing – if in doubt, ask your seller.

What happens if I skip the suction filter before the pump?

Nothing may happen in the short term – especially if the water is relatively clean. But in the long run: abrasive sand and stone particles will wear down the impeller and pump bearings. The pump will start to lose performance, make noise, and eventually fail. Repairing or replacing the pump costs dozens to hundreds of euros, while a suction filter costs only a fraction of that. From an economic perspective, skipping the suction filter is one of the most expensive mistakes when installing a home water system. This is discussed in detail in the article Suction filter before the pump: why a sediment filter is essential for a home water system.

Conclusion: how to choose the right filtration

Selecting the right combination of microns is not rocket science, but it does require some systematic thinking. The answer to the question "which microns do I need?" depends on three things: where in the system the filter is installed (before or after the pump), what the actual quality of your water is (a water analysis will show this), and what purpose the water is used for (garden, bathroom, drinking).

As a basic setup for the vast majority of households with a well, the proven rule applies: 120 mcr as a suction filter before the pump, 50 mcr as the first pressure filter after the pump, and 10 mcr as a second stage where needed. This three-stage combination covers 90% of the situations we encounter in practice.

If you are unsure which setup is right for your specific case, check out other articles in our Knowledge Center – especially How to choose a filter for well water: what to focus on before buying and Common questions about water filters: microns, replacement intervals, insert compatibility. These articles will help you make an informed decision without unnecessary overpayment or an underdimensioned system.

Do you have a question about this topic?

Having trouble deciding or dealing with a specific situation in your household? Write to us – we are happy to help.