How does a water filter work? Explanation (2026)

Published on July 21, 2026 | Reading time: ~11 minutes

You turn on the tap and clear water comes out. But between the source and your glass, a series of natural and chemical processes occur that most people never see. When you install a filter, a final, crucial step is added. The question "how does a water filter work" has a surprisingly concrete answer, and that answer determines whether your filter truly does what it promises.

In this guide, we explain step-by-step how a water filter works, what techniques exist, and why the combination of techniques makes all the difference. At PureFilter, we see that customers who understand this make much more informed choices and are rarely disappointed.

1. What is a water filter?

Important to know: a water filter does not make water "sterile." The goal is to reduce contaminants to safe or immeasurable levels, while keeping the water drinkable and, with the right technique, also rich in minerals. Dutch tap water is already of high quality, but between the pumping station and your tap, all sorts of things can be added via old pipes and faucets.

2. How exactly does a water filter work?

The core is simple: water is forced under pressure (the pressure from your water supply) through a filter cartridge. This cartridge contains different layers, each with its own task. The water moves from the coarsest to the finest layer, so that each layer precisely retains what it is good at.

You can compare it to a sieve with progressively smaller meshes, but smarter. A coarse layer catches sand and rust. A carbon layer binds chlorine and organic chemicals to itself. An ion exchanger swaps harmful metals for harmless ions. And with a mineral filter, a final layer actually adds healthy minerals. All these steps happen in a few seconds, as the water flows through the cartridge.

The effectiveness depends entirely on which layers are present and how well they have been tested. A filter with only a carbon layer improves taste, but largely allows heavy metals to pass through. That's why when purchasing, you always look at the certification, more on which later.

3. The 5 most important filtration techniques

Virtually every water filter uses one or more of these five techniques. They differ greatly in what they can handle.

1. Mechanical filtration

The simplest form. Water passes through a physical medium (ceramic, fiberglass, or fine mesh) that traps particles based on size. Sediment, sand, rust, and other suspended particles are left behind. Mechanical filtration says nothing about chemical purity; it removes what you might or just barely not be able to see with the naked eye.

2. Activated carbon (adsorption)

Activated carbon has an enormous internal surface area: one gram can have a surface area of more than 1,000 square meters. Chemical substances such as chlorine, pesticides, and volatile organic compounds adhere to that surface, a process called adsorption. This is the technique that provides better taste and odor, and also retains some heavy metals and PFAS.

3. Ion exchange

In ion exchange, a resin swaps harmful ions (such as lead, nickel, or nitrate) for harmless ones. This technique is crucial for effectively removing heavy metals and reducing water hardness. Without ion exchange, a filter allows many dissolved metals to pass through.

4. Reverse osmosis (RO)

The most radical technique. Water is forced under high pressure through a semi-permeable membrane that retains almost everything: metals, salts, chemicals, and microorganisms. The result is extremely pure water. The downside: RO also removes healthy minerals like calcium and magnesium, consumes 3 to 4 liters of wastewater per liter of drinking water, and requires a more complex installation. Read more in our guide on the RO water filter.

5. Remineralization

The technique most filters lack. After the water is purified, a mineral layer adds calcium, magnesium, and potassium back. This improves taste and contributes to your daily mineral intake. The PureFilter Mineral+ uses Swedish Mineral Rock™ technology for this, so filtered water does not taste "empty" as with pure RO.

4. Why should you use a water filter?

Dutch tap water is among the best in the world and is strictly controlled by drinking water companies and the Human Environment and Transport Inspectorate. Nevertheless, more and more households are opting for a filter, and there are concrete reasons for this:

• Old pipes: houses built before 1960 may still have lead internal pipes. Water that sits in them absorbs lead. According to the Drinking Water Platform, in a small portion of tap water samples, the lead standard is exceeded.
• Chlorine taste: in the Netherlands, tap water is generally supplied without chlorine, but in some situations or during malfunctions, chlorine is temporarily added, which affects the taste.
• New contaminants: substances like PFAS and microplastics have only recently been seriously mapped and are not yet incorporated into all standards.
• Less bottled water: a filter saves hundreds of plastic bottles a year and is much cheaper in the long run than bottled water.

5. The benefits at a glance

• Safety: a certified filter removes over 100 contaminants, including lead, arsenic, PFAS, and chlorine by-products.
• Taste: no more chlorine taste and musty odors, plus a fresh mineral taste with remineralizing filters.
• Convenience: an inline filter sits under your sink and continuously provides filtered water, without refilling pitchers or carrying bottles.
• Cost: with a capacity of 15,000 to 20,000 liters per cartridge, a liter of filtered water costs a fraction of bottled water.
• Environment: hundreds fewer plastic bottles per household per year.

6. Points of attention

A filter only works well if you keep a few things in mind:

• Replace the cartridge on time: a saturated filter stops filtering and can even release accumulated substances. Replace the PureFilter cartridge every 12 months or after 15,000 to 20,000 liters. Replacement filters are available from €49.90.
• Rinse after stagnation: if the water has been stagnant for more than 3 days (for example, after a holiday), let the tap run for 30 seconds before drinking.
• Pay attention to certification: not every filter that makes claims has been independently tested. NSF 53 is the international standard for lead removal, among other things.
• Choose the right technique: if you only want to improve the taste, carbon is sufficient. If you really want to remove heavy metals, you need ion exchange or RO.

7. Comparison table: filter types side by side

8. How does the PureFilter Mineral+ work?

The PureFilter Mineral+ is an inline filter that connects to your cold water line under your sink. It combines three techniques in one cartridge, so you don't need multiple separate systems.

• Step 1, activated carbon: binds chlorine, PFAS, medicine residues, pesticides, and organic chemicals.
• Step 2, ion exchange: removes heavy metals such as lead, arsenic, nickel, and cadmium.
• Step 3, Swedish Mineral Rock™: adds calcium, magnesium, and potassium back for a fresh, mineral-rich taste.

The result: water purified of over 100 contaminants AND tastes good, instead of the "flat" water that pure reverse osmosis produces. At PureFilter, we see that customers who previously had an RO system actually switch because their water regained its taste. The filter is certified to NSF 42, 53, 61, and 372, and installation takes 5 to 10 minutes without a plumber.

9. Buying advice: which filter is right for you?

The right choice depends on what you want to achieve:

• Do you primarily want better taste? A carbon filter or filter jug is sufficient, but keep in mind their small capacity and limited range.
• Do you really want to remove heavy metals? Choose an NSF 53-certified inline filter such as the PureFilter Mineral+, which filters continuously without intermediate maintenance.
• Do you live in a rental property? An inline filter can usually be installed without major modifications, but first read our guide on the water filter in a rental property.
• Still in doubt? Take the test in our guide which water filter suits me or check out our page best water filter.

For most Dutch households, the PureFilter Mineral+ offers the best balance between filter performance, ease of use, and taste. Also check out the complete range on our page water filter for home. Do you have any questions? Check the frequently asked questions.

10. Frequently asked questions about how a water filter works

11. Conclusion

A water filter works by guiding water through successive layers, each with its own task: retaining particles, binding chemicals, exchanging heavy metals, and, with better filters, adding healthy minerals. Which substances actually disappear depends entirely on the techniques used and the certification.

If you want both safety and taste, a certified inline filter with remineralization is the smartest choice. The PureFilter Mineral+ combines carbon, ion exchange, and Swedish Mineral Rock™ in one cartridge, is certified to NSF 42, 53, 61, and 372, and can be installed in 5 to 10 minutes. Want to know more? Visit purefilter.nl.