Frequently asked questions about water filtration at home
Water filtration at home: answers to the most frequently asked questions our customers ask
Over the years of working with water supply and filtration systems, we have heard hundreds of questions from customers. Some of them repeat so regularly that we decided to gather them together and answer them honestly, with real numbers and practical examples. This article is not a marketing brochure – it is a summary of what really works, what people underestimate and where mistakes are most commonly made.
If you are interested in a specific area of filter selection, also see our article How to choose a water filter for the home: a complete guide, where we go into even greater depth. Here we focus on answers to specific questions that people actually ask – including those they are too embarrassed to ask salespeople.
Basic concepts: what filtration is and what it is not
The first obstacle we encounter in every consultation is the mixing of terms. Filtration, softening, disinfection and water treatment are not the same – and correctly naming the problem is half the solution.
What exactly does a water filter do?
A water filter mechanically or chemically captures unwanted substances from water. Mechanical filters capture solid particles – sand grains, rust flakes, silt, sediment. Chemical or adsorption filters (e.g. with activated carbon) capture dissolved organic substances, chlorine, pesticides, some metals. Biological contamination – bacteria, viruses, protozoa – is usually not destroyed by standard filters. For this, UV disinfection or chemical disinfection is used. More on this distinction can be found in the article UV water disinfection: when a filter is not enough and you need a UV lamp.
A water softener is not a filter – it is an ion exchanger that replaces calcium and magnesium ions with sodium ions. Hard water after that will be soft, but if it contains, for example, iron in oxidized form, the softener will not remove it – on the contrary, it may partially capture it and deposit sludge. The topic of softening is discussed in more detail in the article Water softening vs. filtration: what is the difference and what do I need.
Do I need to have a water analysis done? Isn't it enough to look at it and taste it?
This is one of the most common questions – and the answer is clear: water analysis is an essential basis. Not a costly luxury, but a necessity. Water can look crystal clear, taste innocent and yet contain elevated levels of nitrates (particularly dangerous for infants), manganese, arsenic or coliform bacteria. On the other hand, slightly brownish water from a well can be microbiologically fine and require only a simple iron filter.
From practice: a customer from the Považie region had slightly yellowish water from a well and asked for "something for iron". When we insisted on an analysis, it turned out that iron was only slightly above the limit (0.28 mg/l at a limit of 0.2 mg/l), but manganese was at 0.18 mg/l (limit 0.05 mg/l) and ammonium ions indicated probable faecal contamination. A simple filter would not have been enough – a combination of filtration and UV disinfection was needed.
We recommend including at least the following in a basic water analysis for a well: pH, turbidity (NTU), hardness, iron, manganese, ammoniacal nitrogen, nitrates, nitrites and microbiology (total colony count, coliform bacteria, E. coli). The cost of such an analysis at an accredited laboratory is around 80–150 €, which is a fraction of the price of a filter you would buy blindly without analysis.
What is the difference between a mechanical filter and a filter with activated carbon?
A mechanical (sediment) filter captures only solid insoluble particles – larger than the size of its pores. Common household sediment filters have a porosity of 5, 10, 20 or 50 micrometres (μm). A 5 μm filter will capture sand grains, rust flakes, silt, but chlorine, pesticides and dissolved metals will pass through it without problems.
A filter with activated carbon (GAC – granulated activated carbon, or CTO – carbon block filter) works on the principle of adsorption. Substances stick to the surface of the carbon. Activated carbon has an enormous active surface – 1 gram can have a surface of up to 1 000 m². It captures chlorine, chloramine, dissolved organic substances, pesticides, herbicides, improves the taste and odour of water. It does not capture nitrates, salts of hardness, most heavy metals in ionized form or microorganisms.
What is KDF medium and why is it interesting for shower filters?
KDF (Kinetic Degradation Fluxion) is an alloy of copper and zinc, which through redox reactions neutralizes chlorine, limits bacterial growth and captures some heavy metals (lead, mercury). Unlike activated carbon, it works even at higher temperatures, which makes it suitable for shower filters – where the water is hot. Our shower filter with KDF 1/2" is therefore a popular solution for people who are bothered by chlorine in the shower – it dries the skin, irritates the eyes and damages hair colour.
Do I need to filter the entire house, or is a filter under the sink enough?
It depends on the issue. If it's just about improving the taste of drinking water, a filter under the sink (so-called sink filter or reverse osmosis under the sink) is a cheap and effective solution. You filter only the water you actually drink – which is a small fraction of the household's total consumption.
If, however, the problem is in your well or at the point of entry into the house (high iron, manganese, turbidity, hardness), these parameters will affect not only drinking water but also laundry, dishwashing, taps, water heater, washing machine, and all appliances. Rust stains in the bathroom, a clogged water heater, cracked tap seals, gray laundry – these are the consequences of not filtering water at the point of entry. In this case, a central filter at the house entrance is necessary.
Typical case: a family from a village near Nitra with their own well. The customer wanted "just some filter under the sink, because the water tastes strange". When we arrived, the water heater was 8 years old and clogged with scale to the extent that its performance had dropped by an estimated 40%. The check valves of the taps were worn out. The washing machine had turbidity in the tank. The problem was not in the taste of drinking water – the problem was in the entire plumbing system. Solution? A central filter for iron and manganese at the entrance, a softener after it, and then a sink filter for drinking water.
Where is the central filter usually installed?
The central filter is installed as close as possible to the point where water enters the house – before the manifold, before the water heater, before all the distribution lines. The standard sequence for a well with complex issues looks like this: sediment pre-filter → iron and manganese filter → softener → UV disinfection → home distribution. More about design and placement can be read in the article Installation of a home water filter: procedure, tools, and most common mistakes.
How long do filters last and when should they be replaced?
This is a question for which there is no one universal answer, but it can be well estimated based on several factors.
Sediment cartridges (PP fibers): usually 3–6 months, depending on the amount of sediment in the water. If you have water from a well with a higher sand or silt content, it can clog in 4–6 weeks. In a municipal water supply, it can last up to 6 months. Indicator: a significant pressure drop after the filter.
Activated carbon (GAC cartridges): 6–12 months with normal consumption, or according to the volume of filtered water (typically 10,000–20,000 liters). Carbon does not clog as visibly as sediment filters – it stops capturing chlorine and organics, but pressure does not drop. Therefore, it is changed according to a time interval, not pressure.
Filtration media in pressure vessels (BIRM, Pyrolox, sand): with proper regeneration, they can last 5–10 years, sometimes even longer. They are not replaced regularly like cartridges – they are regenerated by backwash. More in the article Maintenance and regeneration of filtration media: how long they last and when to replace.
UV lamps: manufacturers recommend replacement after 9,000 hours of operation, which corresponds to approximately 12 months of continuous lighting. The lamp may still glow after this time, but the intensity of UV radiation drops below the effective threshold. Quality replacement parts such as UV lamp Viqua S463RL guarantee the correct spectrum and performance throughout the entire lifespan.
Is hydrogen water just a fashion myth, or does it have real benefits?
This is a topic where it is important to distinguish between verified studies and marketing claims. Molecular hydrogen (H₂) dissolved in water has proven antioxidant properties – it is small enough to pass through cell membranes and neutralize reactive forms of oxygen (free radicals). There are studies – mainly Japanese and Korean – that suggest a positive effect on inflammatory processes, fatigue during physical exertion, and certain metabolic parameters.
What is clear, however, is that hydrogen water is not a substitute for filtration. If you have iron, manganese, bacteria, or hardness in your water, hydrogen water does not solve these problems. It is an addition for people who are interested in optimizing their lifestyle and have the basic water quality already resolved. Our hydrogen water generator HYDRO is intended precisely for this group – people who want something extra in addition to regular clean water.
What is a water softener and do I really need it?
A water softener removes calcium (Ca²⁺) and magnesium (Mg²⁺) ions from water using an ion-exchange resin, replacing them with sodium ions (Na⁺). The resin is periodically regenerated with brine – hence the salt in water softeners.
Water hardness is expressed in mmol/l, °dH (German degrees), or mg/l CaCO₃. Approximate classification: soft water up to 1.25 mmol/l (7 °dH), moderately hard 1.25–2.5 mmol/l, hard 2.5–3.75 mmol/l, very hard above 3.75 mmol/l. A large part of Slovakia – including Bratislava and southern Slovakia – has water hardness above 2.5 mmol/l.
You really need a water softener if: you have visible scale deposits on taps and showerheads, frequent water heater clogging, laundry issues (gray clothes, high detergent consumption), or if a laboratory analysis confirms hardness above 2 mmol/l. Automatically controlled softening head 1" – HYS-1 is a solution that handles the entire regeneration process automatically according to a programmed schedule or volume of filtered water, without manual intervention.
Can a water softener harm your health?
Concerns about excess sodium in softened water are understandable. Real numbers: hard water at 25 °dH softened to 4 °dH will contain approximately 180 mg of sodium per liter – which is about 360 mg of Na extra per day with 2 liters of consumption. The recommended daily sodium intake is 2,300 mg (WHO), so the increase is relatively small, but for people on a low-sodium diet or with hypertension, it is worth consulting a doctor. An alternative is a softener with a different regenerant (potassium instead of sodium), but these are more expensive to operate.
Why does my well water smell like sulfur (rotten eggs)? Will a filter help?
The smell of hydrogen sulfide (H₂S) – that characteristic smell of rotten eggs – is a fairly common issue with wells, especially in areas with higher organic content in the soil or where geological changes have occurred. The source is either hydrogen sulfide directly in the groundwater or sulfate-reducing bacteria that convert sulfates into H₂S.
The solution depends on the cause and concentration. For low concentrations of H₂S (up to about 0.5 mg/l), air venting or an activated carbon filter may help. For higher concentrations or biological causes, a combination is necessary: oxidation (with air or chemically), filtration, and UV disinfection. This is a case where water analysis is not enough – you also need a microbiological and sulfate analysis.
Why do I still taste chlorine in the water after installing a filter?
If you have installed a carbon filter and still taste chlorine, there are several possible reasons:
- The new filter was not flushed: new carbon filters need to be flushed for 5–10 minutes with clean water until the fine carbon particles settle and the medium is activated.
- The filter is exhausted: if you didn’t install it yourself, check when it was last replaced. Carbon has a limited adsorption capacity.
- Chlorine concentration is too high: city water in the summer, when the water supply contains more organic matter, often has higher chlorine levels. A simple filter may not be able to capture it at high flow rates.
- Chloramine instead of chlorine: some water companies have switched to chloramine (NH₂Cl), which is more resistant to standard activated carbon and requires special catalytic carbon (Catalytic Carbon).
How much does it cost to operate a home water filter?
Operating costs are a topic that customers rarely ask about – and then are sometimes unpleasantly surprised. Let’s break it down for typical scenarios.
A simple two-stage filter (sediment + carbon) for city water: two filters per year (sediment every 6 months, carbon once a year) = about 15–35 € per year. Minimal maintenance, minimal costs.
A central iron filter with automatic backwash: energy for the pump during regeneration (about 2–4 times a month, each cycle about 20–30 minutes) = negligible. Water consumption for rinsing: about 50–100 liters per cycle = about 600–2 400 liters extra per year. The medium does not need to be replaced – only inspected. Operating cost: about 2–5 €/year for energy and water.
Water softener: the main operating cost is salt. A typical 4-person household consumes 80–150 kg of salt per year (depends on water hardness and consumption). Cost of regenerant salt: 0.30–0.50 €/kg = about 30–70 € per year. Plus energy for the control unit (a few €/year).
UV disinfection: the UV lamp usually runs continuously. Power consumption of a typical unit for a household: 17–40 W. At 0.20 €/kWh, this is about 25–70 € per year for electricity. Plus lamp replacement once a year (lamp price 40–100 € depending on type – e.g., UV lamp Viqua S463RL).
How can I tell if my iron filter is actually working?
This is a practical question that everyone who has an iron and manganese water filter installed asks. The most reliable way is repeated water testing – take a sample before the filter (raw water) and after the filter (filtered water) and compare the values. If the filter is working properly, iron after the filter should be below 0.2 mg/l and manganese below 0.05 mg/l.
Visual indicators that the filter is not working or needs attention: rust stains on the sink, yellowish discoloration of water after standing for a long time, cloudiness in a white glass. Reasons for malfunction: clogged medium (backwash needed), too low pH of the incoming water (BIRM requires at least pH 6.8), too high organic content (clogs the medium), or flow rate too high for the filter’s capacity. More on diagnostics in the article Common water filter problems and how to fix them.
Can a water filter also damage the water?
Yes – and this is a topic that is talked about far too little. A filter that is not properly maintained can be a source of microbiological contamination. Carbon cartridges that are not replaced for a long time can become a breeding ground for bacteria – the medium retains moisture and organic matter that the bacteria capture. If bacteria then grow directly in the cartridge, the water after the filter can be microbiologically worse than the water before it.
This is not a theoretical problem. We have encountered cases where customers had a filter installed for 3 years without replacing the cartridge and the water analysis after the filter showed a significantly increased number of colonies. Therefore: follow the recommended replacement intervals, when the system is idle for a longer period (holiday, cottage) drain and flush the water before use, and never install a simple carbon filter where there is microbiological contamination – always combine it with UV disinfection.
Reverse osmosis – is it overkill for a regular household?
Reverse osmosis (RO) is a membrane technology that captures almost everything – salts, heavy metals, nitrates, pesticides, bacteria and viruses. The result is water with total dissolved solids (TDS) typically below 20–50 mg/l (drinking water has a limit of 1 000 mg/l, and regular tap water is usually 200–500 mg/l).
When you really need RO: high nitrates (over 50 mg/l), elevated arsenic, contaminated water in industrial areas, baby water with guaranteed low values. When it might be unnecessary: if you have regular city tap water and you just want to improve the taste – a good carbon filter may be sufficient.
Disadvantages of RO: slow water production (typically 150–400 ml/min), waste water (2–4 liters of waste are generated for every liter of drinking water), the need for a storage tank, remineralization (RO water is demineralized and needs to be supplemented with minerals for optimal taste and health properties).
Most frequently asked questions (FAQ)
Can I drink water from my own well without a filter?
Technically yes, but legally it is your responsibility. A well is not controlled by a water utility and its quality depends on local geological conditions, distance from agricultural fields, septic tanks and manure pits. We recommend having a water analysis done at least once a year (microbiological results vary seasonally) and deciding on a filtration solution based on the results. Drinking well water without analysis is a risk that may not show up in the short term, but can have consequences in the long term – especially with nitrates, manganese and arsenic.
Why does my water taste salty after the water softener?
A salty taste after the water softener usually indicates one of three problems: incorrectly set regeneration cycle (too much brine remains in the resin), a fault in the control valve (not rinsed after regeneration), or a too short rinse cycle. Softened water should not taste salty – sodium content is indeed higher than before softening, but not enough to be noticeable. If the water tastes salty, it is a malfunction, not a normal condition. Check the settings of the control head and the length of the rinse cycle.
How do I determine what flow rate filter I need for my household?
Basic rule: the maximum instantaneous flow rate of the household is estimated as the sum of all simultaneously used outlets. A typical 4-person household with two bathrooms, a kitchen and a washing machine can have an instantaneous flow rate of 20–30 liters per minute when multiple devices are running at the same time. A central filter must be able to handle this flow rate without a significant drop in pressure. A detailed calculation with tables can be found in our article What flow rate filter do I need: calculating capacity based on household consumption. Remember: a filter that is dimensioned too tightly will clog quickly and will reduce pressure throughout the entire system.
Is it worth investing in an expensive filter or is a cheap one enough?
It depends on the problem and how you use the filter. A cheap sediment pre-filter for €10 can be an ideal solution if you have only mild turbidity from the water supply. But if you have iron at double the limit and manganese, a cheap solution won't help – you will buy something that doesn't work and in a year you will solve the problem again plus deal with a damaged water heater. From experience: customers who didn't want to spend more than €50 on filtration typically invest hundreds of euros more within two years to repair devices damaged by the water. A proper analysis + a properly dimensioned system always pays off in the long run.
Can I use an iron filter for manganese as well?
It depends on the filter media. BIRM can handle both – but manganese requires a higher pH (ideally 8.0+) and lower organic load. Katalox Light and Pyrolox are more effective for manganese than BIRM, as they work even at lower pH and higher concentrations. If you have both iron and manganese (a common case), a combination of media or a properly selected filtration system, such as our water filter for iron and manganese HydroTreat BIRM, is specifically designed for this case. A comparison of media can be found in the article BIRM vs. Pyrolox vs. Katalox Light: comparison of iron filtration media.
What should I do if I go on a long vacation and have a filter at home?
For an unoccupied household (2 weeks or more), we recommend: closing the water supply to the house (if possible), flushing the filter before leaving, and letting the water run for 5–10 minutes after returning before use, to flush out any stagnant water from the pipes and the filter. You can turn off the UV lamp – but when turning it on, let it warm up for 5 minutes before passing water through the reactor. For cottages with seasonal use, it is also suitable to disinfect the system with chlorine once per season, followed by a thorough rinse.
Conclusion: water filtration is not a luxury, but prevention
Water filtration in the household is a topic that affects health, appliance lifespan and long-term financial costs. Mistakes in selection or neglect of maintenance have real consequences – from damaged appliances through reduced drinking water quality to health risks. The correct approach always starts with a water analysis, continues with selecting a system to measure and includes regular maintenance.
If you have read this article and are still unsure what exactly your situation requires, check out other articles in our Knowledge Center – for example Iron and manganese in water: how to detect the problem and choose the right filter or How to choose a water filter for your household: a complete guide. Every scenario is a bit different, but the basic principle remains the same: first know what to filter – then choose how.
Do you have a question about this topic?
Not sure how to decide or dealing with a specific situation in your household? Write to us – we are happy to help.