How to choose a well water filter: what to focus on before buying

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How to choose a water filter for a well: what to focus on before buying

Well water is not the same as tap water. It has not passed through a treatment plant and carries with it what it has passed through in the ground, which can be very diverse – from fine sand and silt through iron and manganese to microbiological contamination. When someone acquires a home water supply or wants to connect a well to the household plumbing, water filtration is a topic they cannot avoid. The problem is that the range of filters and cartridges appears confusing at first glance: different sizes, different microns, simple or double filter, washable or single-use cartridge, pre-pump or post-pump filter...

This article will help you go through the whole topic systematically, without shortcuts and unnecessary simplifications. The goal is for you to know exactly what your well needs, which filter to buy, where to connect it, and what to expect from it after reading it.

Why well water filtration is a different category from tap water filtration

Water from the public water supply has already been treated when it reaches your home. The treatment plant takes care of sediment, microorganisms, and basic chemical treatment. Your home filtration may have dealt with hardness or chlorine only. With a well, none of that applies. You are the operator of your own water supply, and the entire responsibility for water quality lies with you.

Well water has several characteristics that make it a filtration challenge:

Sediment content – sand, silt, mud, fine mineral particles. The amount depends on the depth of the well, the condition of the concrete rings, and the situation after rain or during the thawing period. I have customers who tell me that "the water looks clean" – and then we see the cartridge after a month. A gray-brown cake of fine silt speaks a different language.
Iron and manganese content – a very common problem in Slovakia. Groundwater is deoxygenated, iron is dissolved in it and transparent. When it reaches the air, it oxidizes and leaves orange-brown stains. A mechanical filter will not catch it in dissolved form; for that, iron removal is needed. However, coarse mechanical filtration at least captures the precipitated flocs.
Water hardness – calcium and magnesium. A mechanical filter will not affect it; for that, a softener is needed. However, when planning the system, you should also think about this.
Microbiology – bacteria, viruses, spores. A mechanical filter will catch them only partially and only at very small microns (under 1 mcr). Usually, a UV lamp or another solution is needed if microbiological contamination is confirmed by analysis.

Filtration is therefore not a one-dimensional matter. A mechanical filter is the basis, but it should be part of a comprehensive solution according to the actual water analysis – not guessing.

The first step before buying a filter: water analysis

I repeat this to every customer who writes to me or calls me: without water analysis, we are just guessing. You can get a water analysis from your local public health office or from an accredited laboratory – usually for 30–80 € depending on the scope. A basic analysis includes physical-chemical indicators (turbidity, color, iron, manganese, hardness, pH, nitrates) and microbiological indicators (coliform bacteria, enterococci).

Based on the analysis results, you will know:

Whether you need only mechanical filtration or also iron removal, softening, UV disinfection.
How fine a filtration you need (50 mcr? 10 mcr? 5 mcr?).
How quickly the cartridge will get clogged and how often it needs to be changed.

If you do not have an analysis and for some reason cannot wait for it, you can start with a coarser filter (50 mcr) and clarify the situation by monitoring the cartridge clogging. It is not ideal, but many people do it this way in practice.

Filter before the pump or after the pump: a crucial difference

This is one of the first things where people make a mistake. There are two fundamentally different situations where the filter belongs, and each requires a different type of filter.

Suction filter – before the pump (suction filter)

If your pump is located outside (a surface pump or a self-priming pump in a pump pit), the suction filter is placed before the pump inlet – on the suction pipe. Its task is to protect the pump from coarse sediment. The pump does not like sand: quartz sand particles act like sandpaper on mechanical parts and bearings.

This position is suitable for the Sand filter 1" 120–130 mcr – suction filter before the pump. It is specifically designed for operation under vacuum (suction conditions), has a durable construction and a coarse filtration of 120–130 microns – thus it captures visible sand grains and larger impurities. Fine filtration is handled by another filter after the pump.

Caution: standard pressure filters with glass vessels (classic Senior type) are not suitable for suction mode. They are dimensioned for operation under pressure, not under vacuum, and could be damaged or the vessel could implode.

Filter after the pump – pressure filtration

Behind the pump (or behind the pressure tank), the filter operates under the pressure of water from the household supply. This is where you can achieve a higher quality, finer filtration. Filters with 10" (ten-inch) cartridges are used here, which are the standard for domestic applications. This position includes, for example, Filter SENIOR 10" MONO with 1" connection or, for higher filtration requirements, Atlas Filtri Senior 10" DUO 1" – a dual filter for two cartridges in series.

Filter cartridge size and connection size: what do these parameters mean

When you look at products in the filter category, you will encounter parameters such as "10"" and "1"". Both are inches, but each refers to something different.

10" (ten-inch cartridge) – refers to the length of the filter cartridge. Ten-inch cartridges (approx. 25 cm) are the absolute standard for domestic filtration systems. They are compatible across different manufacturers (with the exception of special types) and are available in a wide range of filter media – from mechanical to activated carbon and even special media for iron. Filters in the Senior 10" category are designed for these cartridges.

1" (one-inch connection) – refers to the diameter of the threaded connection of the filter to the pipe. A diameter of 1" (external thread G1") is the standard for household water supplies and domestic water systems. It corresponds to the flow rate required by a typical household water supply (pump 50–100 l/min). Larger diameters are used for higher flows (industrial, agricultural applications).

Read more about these parameters in the article Filter cartridge size 10" and connection size 1" – what do these parameters mean, which you can also find in the Knowledge Centre.

Micros: what filters 120, what 50 and what 10 microns

A micron (µm, micrometre) is a measure of the pore size of the filter cartridge – in other words, the smallest particles that the cartridge can capture. The lower the number, the finer the filtration. However, note – finer filtration does not always mean better. A finer cartridge clogs faster, significantly restricts the flow, and with a high sediment content can be practically unusable.

In practice, it looks like this:

120–130 mcr: suction filter before the pump. It captures visible sand and coarse particles. It is sufficient for pump protection.
50 mcr: first stage of fine filtration after the pump. Suitable as a pre-filter in a DUO system or where the water is relatively clean and mainly sand contamination is present. A washable insert Mechanical insert 10" RL SX 50 mcr washable is a good choice here – it can be rinsed and reused.
10 mcr: finer filtration, captures muddy sediment, fine dust, and settled iron flocs. A one-time use wound insert Mechanical insert 10" FA 10 mcr wound is a typical example – higher filtration efficiency, but it is replaced after clogging.

A detailed comparison of the values 10, 50, and 120 microns can also be found in a separate article Mechanical water filtration: comparison of 10, 50, and 120 micron inserts in the Knowledge Centre.

MONO or DUO filter: when one is enough and when two stages are needed

A simple (MONO) filter has one body with one insert. A double (DUO) filter has two bodies in series, each with its own insert. Both types have their place, and the choice depends on the quality of your well water.

A MONO filter is sufficient where the water is not significantly contaminated with sediment, turbidity is low, and iron content is within acceptable limits. For example, if the analysis shows only slightly increased turbidity and minimal sand content, a single filter with a 10 mcr insert is enough. The SENIOR 10" MONO filter is completely sufficient for such a scenario.

A DUO filter is a solution for water with more pronounced contamination or where you want a longer service interval (a finer insert in the second stage is protected by a coarser one in the first and clogs more slowly). A typical DUO setup: first stage 50 mcr washable SX insert (captures coarse sediment, can be rinsed), second stage 10 mcr wound insert (fine filtration). This tandem makes sense with more abundant sand or silt in the well.

The topic of MONO vs. DUO is discussed in more detail in the article What filtration is sufficient for me: MONO vs. DUO filter – difference and when to use what, which you can find in the Knowledge Centre.

Washable or disposable insert: practical considerations

This is a question I receive very often: "Is it worth buying a washable insert so I don't have to buy a new one every month?" The answer is not straightforward – it depends on the conditions.

Washable insert SX (e.g., type RL SX 50 mcr) has a plastic/stainless steel frame with a filtration mesh. When it gets clogged, we remove it, rinse it under water pressure or with a soft brush, and put it back. The lifespan of such an insert is several seasons under normal load. The advantage is clear: you save on insert consumption. The disadvantage: coarser filtration (50 mcr), so it is not sufficient for fine filtration. In addition, the insert must be cleaned thoroughly – insufficient cleaning can lead to bacteria growth.

Disposable wound insert (e.g., type FA 10 mcr) is a wound polypropylene or cotton around a rigid core. When clogged, it is discarded and a new one is inserted. The advantage: it achieves fine filtration (5–10 mcr) at an acceptable insert cost (usually 2–5 €), is sterile from the factory and cannot contaminate water due to improper cleaning. The disadvantage: you need to regularly buy replacements.

From practice: for a well with significant sand and silt, I recommend a combination – a washable 50 mcr as the first stage in a DUO filter (saves on insert costs, as it is only rinsed) and a disposable 10 mcr as the second stage (fine filtration, replaced once every 2–4 months). This is a proven and economically reasonable combination.

Materials, pressure resistance, and temperature: what to pay attention to when selecting the filter body

The filter body itself (container, lid, head with connections) must be dimensioned for the conditions in which it will operate.

Pressure: Standard household water systems operate at a pressure of 2–4 bar (adjustable on the pressure switch). Standard filter bodies are dimensioned for a maximum of 6–8 bar. If you have an above-standard high pressure (e.g., pump set to 5–6 bar), check the maximum operating pressure of the filter in the technical documentation.
Temperature: Most plastic filter containers for well water are designed for cold water (max. 30–40 °C). For hot or domestic hot water, a different body is required.
Material: Standard bodies are made of food-grade ABS or polypropylene. Transparent containers allow visual inspection of the insert clogging without disassembly – very practical.
Seals: The filter must be sealed. Rubber O-rings are part of the filter, but during installation, they must be properly placed and possibly lightly greased with vaseline. A water leak at the container location is most often caused by a shifted or damaged O-ring.

Where to install the filter: location, bracket, accessibility

The filter should be placed in a location where it is easily accessible for insert replacement. Ideally, it should be in a dry, cool, and non-freezing place – boiler room, technical room, or a protected wall in a storage room. The filter must not freeze: water expanded by freezing will tear the filter container just as reliably as cast iron piping.

It is always mounted vertically – the container hangs down. The filter head is at the top, with water inlet on the left ("IN") and outlet on the right ("OUT"). If you reverse this, the filter will not function properly and you may damage the insert.

The filter is attached to the wall with a bracket (usually included in the package). For a DUO filter, both bodies are mounted next to each other on a common bracket or each separately, but closely behind each other so that the outlet of the first is directly the inlet of the second via a short coupling.

A detailed installation procedure can be found in the article Wall mounting of a water filter step by step: bracket, connection, sealing.

How to Determine the Replacement Interval of a Filter Cartridge

Another practical question: how often to replace the filter cartridge? There is no universal answer to this – it depends on the water quality, flow rate (how much water you filter daily), and the fineness of the filter.

Estimated intervals from practice:

50 mcr washable filter cartridge: cleaning every 4–8 weeks with normal well water containing sandy sediments. Replacement after 2–3 years or when the mesh is damaged.
10 mcr wound filter cartridge: replacement every 2–4 months under normal load. Earlier if there is heavy contamination (mud, silt after rain).
120 mcr suction sediment filter: cleaning as needed, monitor the drop in pump suction performance as an indicator of clogging.

The most reliable indicator of filter cartridge clogging is a drop in pressure at the filter outlet. If you have pressure gauges before and after the filter, you can see the pressure difference (delta P). With a new filter, delta P is minimal (under 0.2 bar), and it increases with clogging. When it reaches 0.5–0.8 bar, it is time for replacement or cleaning. Without pressure gauges, monitor practical signs: weak flow from taps, longer tank filling times, and a whining pump running dry.

The topic of cleaning and replacing washable filter cartridges is discussed in more detail in the article Washable Filter Cartridges for Well Water: How and When to Clean and Replace Them.

Common Mistakes in the Selection and Installation of Well Water Filters

Over the years of practical experience, I have seen several recurring mistakes. I mention them so you can avoid them:

Purchasing a filter without water analysis: The most common mistake. A customer buys a 10 mcr filter, but the water is so muddy that the filter lasts only three days. Or, conversely, they buy a 50 mcr filter, but the water contains such a high amount of fine silt that 50 mcr is insufficient.
Forgetting the suction filter before the pump: Many people buy only a filter after the pump and do not protect the pump itself. After one or two years, they wonder why their pump is whining and losing performance – damaged impeller.
Mounting a standard pressure filter on the suction line: As I mentioned, a pressure filter is not designed for vacuum. Immediate implosion of the tank upon the first pump start. (Yes, I have actually seen this.)
Reversed flow direction: A filter mounted backwards (inlet and outlet swapped). The filter cartridge gets clogged from the wrong side, and filtration is inefficient.
Lack of a ball valve before the filter: When replacing the filter cartridge, you must shut off the water supply. Without a valve before the filter, you have to turn off the entire pump and release pressure from the whole system – unnecessarily complicated.
Unsealed threaded connections with hemp or Teflon: Water leakage at threaded connections. Threads must be sealed with hemp and paste or Teflon tape – at least 4–5 wraps.

Price Orientation: What You Will Actually Pay

A filtration system for well water is not an expensive matter – if you know what to buy. Estimated prices (without installation):

Suction sediment filter: 15–30 €
MONO filter Senior 10" with cartridge: 25–50 €
DUO filter Senior 10" with two cartridges: 50–90 €
Disposable wound cartridge 10" (10 mcr): 2–6 € / pc
Washable cartridge SX 50 mcr: 8–15 € / pc (but lasts for years)

Annual costs for filter consumption in a typical family home (4 people, approx. 300–400 l/day): expect to spend 20–40 € per year with a combination of washable and disposable cartridges. Not much for the certainty that your pump and pipes are not being damaged by sand.

Special Situations: What to Do If the Water Analysis Reveals More Issues

Mechanical filtration only addresses sediment – sand, silt, mud, and settled flocs. If the analysis reveals additional issues, a mechanical filter alone is not sufficient:

Elevated iron (over 0.2 mg/l): An iron filter (oxidizing filter with manganese sand or aeration) is needed. A mechanical filter will catch only settled flocs, not dissolved iron.
Hard water: A water softener with ion exchange resin. A mechanical filter does not affect hardness.
Microbiological contamination: A UV lamp or chlorination. No mechanical filter reliably eliminates bacteria – only cartridges under 0.2 mcr (absolute filtration) can do that, but that is an industrial device, not a household filter.
Nitrates: Reverse osmosis or an ion exchange unit. A standard filter will not catch them.

In such cases, a mechanical filter is still the first step (protecting other equipment from clogging), but it is not a complete solution on its own.

Practical Scenario 1: A Simple Well at a Family Home

Customer: a family home in the countryside, 8 m deep well, surface pump (water tank) in the utility room. Analysis: slightly elevated turbidity, noticeable sand content, iron 0.08 mg/l (under the limit), microbiology in order.

Recommended solution: a suction sediment filter 120 mcr before the pump + a MONO filter Senior 10" with a wound 10 mcr cartridge after the pump. Total cost under 70 €, cartridge replacement every 3 months (approx. 3–4 €). Simple, reliable, and low maintenance.

Practical Scenario 2: A Well with Significant Mud and Sand

Customer: a garden colony, 5 m deep well, after every heavy rain the water is turbid and full of mud. Analysis: high turbidity, fine silt, high sand content. The customer complains that the cartridges last only 3–4 weeks and the pump has damaged impellers after a year.

Recommended solution: a suction sediment filter 120 mcr before the pump (priority – pump protection) + a DUO filter Senior 10" after the pump: first stage – washable 50 mcr cartridge (cleaned by flushing every 3 weeks), second stage – wound 10 mcr cartridge (replaced every 6–8 weeks, as it is protected by the first stage). The cost of cartridges is significantly lower than with a MONO filter with 10 mcr cartridges alone.

Most Frequently Asked Questions (FAQ)

Do I need a filter even with a deep artesian well? The water looks clean.

Yes, even artesian water can contain fine mineral particles, or elevated iron or manganese. "Looks clean" does not mean it is problem-free – turbidity caused by fine silt may not be visible in a glass, but after filtration you can see a dark brown cartridge. In addition, without mechanical filtration, you have no pump protection. I recommend at least a simple filter after the pump and monitoring cartridge clogging.

Can I use only a suction filter without another filter in the house?

A suction filter is designed for coarse filtration 120–130 mcr – it catches visible sand, but not fine silt, mud, or iron oxides. This is definitely not enough for drinking purposes. A suction filter protects the pump, not you. There should always be at least one finer filter after the pump.

What is the difference between a wound and a pleated filter cartridge?

A wound filter cartridge (e.g., type FA) is wound polypropylene around a solid central core – it has a depth filtration effect, meaning particles are caught not only on the surface but also within the material. It lasts longer under the same load. A pleated filter cartridge is a folded filter membrane with a larger filtration surface – higher flow rate, but shallower particle capture. The choice depends on the specific application; wound cartridges are more common and proven for well water.

Can I use a Senior 10" filter for hot water?

Most plastic filter housings of the Senior series are designed for cold water – the maximum temperature is usually 30–40 °C. For hot utility water or at the outlet of a water heater, you need a filter with a metal or special high-temperature housing. Using a standard plastic filter for hot water can lead to deformation of the housing and leakage.

What to do if the filter leaks when tightening the housing?

The first cause is almost always a shifted or damaged O-ring – the rubber seal between the housing and the filter head. Disassemble the housing, check the O-ring (it should be flexible, without cracks, and properly seated in the groove), lightly grease it with food-grade vaseline, and re-tighten. If the leakage continues after replacing the O-ring, check the seating surface of the filter head for damage or dirt.

How many filters do I need if I have water for garden irrigation?

If you want to filter only the water for household use (drinking, cooking, bathroom), a filter for the garden circuit is not necessary – plants can handle non-filtered well water. Connect the filters only to the household branch after the garden circuit branch. This will save the capacity of the insert and extend the replacement interval, as only a fraction of the total consumed water will pass through the filter.

Conclusion: a systematic approach pays off

Selecting a filter for well water is not rocket science, but it does require a systematic approach. The most important step is water analysis – without it, you are buying blindly. Once you know what the water contains, everything else follows logically: where to place the filter (before the pump, after the pump or both), what filtration fineness to choose, whether a MONO or a DUO filter is sufficient, and whether a washable or disposable insert is more suitable.

The good news is that a basic filtration system for a family house is not expensive – we are talking about an investment under 100 €, which protects a pump worth hundreds of euros and ensures better water quality for the whole household. With regular maintenance and timely replacement of inserts, the system is trouble-free for years. And if you encounter a more complicated situation – high iron content, hard water, microbiological issues – a mechanical filter is always the first step, followed by further technologies.

Find the complete range of filters and filter inserts for well water in the Water Filters category.

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.