3-in-1 or 4-in-1 tap: what is the difference?

Reading time: approximately 9 minutes

What is a 3-in-1 tap?

The 3-in-1 tap is the most well-known type of boiling water tap and effectively replaces your kettle. You dispense boiling water instantly for tea, coffee, pasta, or blanching vegetables, and you no longer need an extra appliance on your countertop. The reservoir under the sink is the heart of the system: it determines how much boiling water you can draw at once and how much power the tap consumes.

Important to know: a 3-in-1 tap is a temperature solution, not a water quality solution. The water that comes out is just your regular tap water, only boiling. Such a tap does not remove limescale, PFAS, or drug residues. If you want that, you automatically end up with the fourth function.

What is a 4-in-1 tap?

A 4-in-1 tap does everything a 3-in-1 tap does, plus one extra function. And therein lies the confusion: that fourth function is not the same for every brand. In practice, you see three variants.

• 4-in-1 with filtered water: cold, hot, boiling, and filtered water. This is the most common version, found in brands like HOWAT, FlexTap, and the Itho Daalderop Close-In More, which combines a 10-liter boiler with a tap that dispenses cold, hot, boiling, and purified water.
• 4-in-1 with chilled or sparkling water: cold, hot, chilled, and sparkling water, such as the Selsiuz Cool 4-in-1. Here, the fourth function is an experience, not purification.
• 4-in-1 with reverse osmosis: cold and hot water plus filtered, filtered boiling, and filtered chilled water. This is the version of the PureAqua 4-in-1 tap, where the water first passes through a reverse osmosis system.

The latter is a fundamental difference. With most 4-in-1 taps, only the cold dispensing point passes through a filter, and the boiling water still comes out of the boiler unfiltered. With a tap based on reverse osmosis, every drinkable dispensing point is filtered, including your tea and your pasta. At PureAqua, we see that customers specifically drop out of cheaper models for this reason: they thought they were buying filtered boiling water and only received a filtered cold tap.

The difference at a glance

In short: the difference between 3-in-1 and 4-in-1 is not about "more luxury," but about what the tap does to your water rather than just its temperature.

Why 4-in-1 means something different for every brand

"4-in-1" is not a protected term or a standard. Every brand decides for themselves which functions count, which explains why prices vary so widely. In a spot check of the Dutch market on August 11, 2026, 4-in-1 taps ranged from approximately 295 euros for an entry-level FlexTap model and 495 euros for a Watura to 1,829 euros for a Selsiuz Cool 4-in-1. A Quooker COMBI+ Flex was priced at about 1,396 euros, and a Quooker Flex with CUBE reservoir as a 5-in-1 at about 2,138 euros.

That price difference of more than a factor of six says more about what happens under your sink. An inexpensive 4-in-1 tap typically has a small boiler and a simple carbon filter cartridge. An expensive tap has a better-insulated reservoir, a carbonation module, or a full-fledged filtration system. The question you should ask every provider is about the technology under your sink: we explain in detail how a filter tap filters your tap water. If you want to evaluate the system yourself, use the criteria from our guide on choosing a reverse osmosis system.

The question you should ask every provider is therefore not "is this a 4-in-1 tap," but: which fourth function do I get, and does the boiling water pass through it too?

What does that fourth channel really filter?

Dutch tap water is of high quality, but there are points of attention. The RIVM advises lowering the PFAS standard for drinking water from 100 nanograms per liter to 4.4 nanograms per liter, expressed as PFOA equivalents, and reports that in more than half of the measurements in drinking water made from river water, the concentration is higher than the 20 percent of the health-based limit recommended by the WHO. This is no reason for panic, but it is a reason to know what your filter is capable of.

Carbon filter: taste, chlorine, and particles

The filter in most 4-in-1 taps is an activated carbon cartridge. This improves taste, captures chlorine and suspended particles, and blocks coarser dirt. It is fine for taste, but it is not a purification technology for dissolved substances like PFAS, nitrates, or heavy metals. We extensively compare the distinction between those two worlds in water filter vs. water purifier vs. reverse osmosis compared.

Reverse osmosis: the finest mesh

Reverse osmosis forces water under pressure through a membrane that stops up to about 99 percent of contaminants, including PFAS, microplastics, heavy metals, and limescale. For this type of system, there is a separate American standard, NSF/ANSI 58, with fixed test procedures for, among other things, the removal of total dissolved solids (TDS); the lead limit in that standard has recently been tightened to 5 micrograms per liter. If you want to know exactly how the technology works, read how reverse osmosis works.

One nuance: reverse osmosis also removes minerals from the water. That is why there is an optional mineral filter that adds minerals back, for a fuller taste. We are honest about that in our article on the disadvantages of reverse osmosis and how to solve them. And because a membrane requires time and pressure, pure water in a 4-in-1 tap is dispensed from a small storage tank instead of directly from the pipe.