Separate tap for filtered water: why? | PureAqua

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Why does filtered water flow through a separate faucet?

Because filtered water is different from the water in the rest of your pipes, and that difference disappears as soon as you let the two mix. A standard mixer faucet is specifically built to mix: hot and cold combine in the faucet body and leave the faucet as a single stream. If you send osmosis water through it, you immediately dilute it again with unfiltered water and lose the purity for which you purchased the system.

On top of that, there are three technical reasons: the pressure behind an osmosis membrane is a fraction of your line pressure, a filter line that is flushed daily remains more hygienic than a line where water sits stagnant, and Dutch installation regulations set requirements for how you connect a filter to your drinking water supply. These four points together explain why almost every serious reverse osmosis system is supplied with its own tap point.

Anyone typing this question into Google rarely finds an answer. The three highest-ranking Dutch pages for this keyword in August 2026 were a brand category, a webshop category, and a product page, with an average of 1,474 words of specifications and prices between 416.17 euros and 605 euros. They show which faucets are available, but none of the three explains why that separate tap point exists at all. We are filling that gap here.

What is a separate faucet for filtered water?

In practice, you see two versions. With the first, you drill a second hole in your countertop, and a slender, often smaller faucet is placed next to it: the classic 1-way tap point. With the second, you keep just one faucet in one hole, but there are two separate channels inside with two controls, where one lever mixes hot and cold and the other opens only the filtered water. That is the 3-way faucet.

The important word in both cases is "separate." The filtered water does not touch the hot water anywhere, not even in the final piece of the spout. At PureAqua, we see that this is precisely the point where customers lose interest in cheap solutions: a little filter that you screw into your existing mixer faucet sounds more elegant, but it provides mixed water by definition. How a filter faucet works internally and which substances such a faucet does and does not block is explained in detail in our article on the operation of a filter faucet.

Four reasons not to send it through your mixer faucet

1. Mixing undoes your purification

Reverse osmosis removes up to approximately 99 percent of dissolved substances from water, from limescale and heavy metals to PFAS and microplastics. The international performance standard for this is NSF/ANSI 58, which deals specifically with household osmosis systems. If you subsequently mix that result with unfiltered tap water, the gain disappears proportionately: half-and-half means that half of everything you removed is back in there.

A mixer faucet cannot prevent that, because mixing is literally its function. There is no setting in which a standard faucet body guarantees that no drop of unfiltered water gets in. A dedicated channel with its own spout is the only construction in which you can be sure of what enters your glass.

2. Warm water damages the membrane

An osmosis membrane is a synthetic film with pores smaller than a nanometer. That film is made for cold tap water. Warm water degrades it and significantly shortens its lifespan, which is why an osmosis system is always connected to the cold water line. If you were to send filtered water through your mixer faucet, the membrane would suddenly be in a line through which hot water can also flow, with backflow being a real risk.

3. The pressure behind the membrane is different

The water that comes through an osmosis membrane, the permeate, has much less pressure than the water going in. A pure water faucet is designed for this: a gentle stream that fills a carafe in half a minute. A standard mixer faucet expects full line pressure and provides a sputtering, unusable stream with a low supply.

That pressure difference also explains why you don't just hang an osmosis system on any existing faucet. Technically, it can only be done with a large pressure tank that keeps the pressure after the membrane at the right level, and such a tank makes the installation more expensive and takes up quite a bit of the already tight space under your sink. The PureAqua system The Source does not have that pressure tank and is therefore not compatible with a boiling water faucet like the Quooker.

4. Hygiene and Dutch installation regulations

This is the point that is not on any sales page, even though the water utility company is explicit about it. Vitens warns that bacterial growth can occur on a filter that is poorly maintained, leading to odor and taste complaints, and advises buying only devices with a quality statement recognized by the Dutch government. Vitens mentions two strict installation requirements: the correct backflow prevention and the premise that any modification to your drinking water installation must comply with the foundations of NEN 1006.

A separate faucet helps with both. The filter line is short, runs only in one direction, and is flushed daily as you use it to fill your glasses and pans. A filter you hang in the middle of your main line, by contrast, sits stagnant for most of the day. And because the filtered circuit remains physically separated from your hot water line, backflow prevention is much easier to get right. Incidentally, Vitens also honestly states that filtering is not necessary for the safety of Dutch tap water; you choose it for the taste, for lime-free water, or to remove specific substances.

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

As soon as you know that the filtered water needs its own channel, the only question left is about the shape. There are three ways to get that channel into your kitchen, plus one solution where you don't modify a faucet at all.

The 1-way pure water faucet

A slender faucet that only provides filtered water and is placed next to your existing mixer faucet. Your existing faucet remains untouched, which is convenient if it is still good or was expensive. You do need a second faucet hole for it. In the PureAqua range, these are models like the AquaPure for 465 euros and the AquaFlow, AquaPulse, and AquaSplash for 495 euros; the compact The Wave is 149 euros. The full series is available under all pure water faucets.

The 3-way pure water faucet

One faucet in one hole, with three flows: hot, cold, and filtered. Two separate channels run inside, and the filtered water exits via its own lever. This is the neatest solution for those who do not want to drill a second hole and still don't want a second faucet on the countertop. Models like The Surge and The Swell start around 590 euros, The Essence is 635 euros, and The Current is 640 euros; The Stream and The Flow are 840 euros. They are listed together in the pure water faucets collection, where the filter system is included with the faucet as standard.

The 4-in-1 faucet

The most comprehensive version: hot and cold water, filtered water, filtered boiling water, and filtered chilled water from a single faucet body. The PureAqua 4-in-1 faucet contains its own reverse osmosis and thus replaces the function of a boiling water faucet. For those who already have a Quooker and still want filtered water, this is the best alternative, precisely because the osmosis system and the boiling water come from the same design. The difference with the better-known 3-in-1 version, which provides boiling but not filtered water, is explained in our article on what a fourth function adds to your faucet.

Not modifying a faucet: the Countertop RO

If you don't want or aren't allowed to change anything in your kitchen, there is a fourth route. The Countertop RO for 495 euros is an osmosis device that stands on the countertop, which you fill with a pitcher and which works without installation. You don't need a second faucet hole, a drill, or any modification to your plumbing, which makes it the standard choice in rental homes. We compare other devices in this category in our overview of devices that create pure water.

Comparing the five setups

The last row deserves a side note. A carbon filter in the main line is the cheapest solution and the only one where you don't get a separate tap point, but it primarily tackles chlorine, odor, and taste. What it does not do is block dissolved salts, nitrate, heavy metals, or PFAS; you need a membrane for that. The RIVM monitors the PFAS situation in Dutch drinking water separately, and that is precisely the type of substance where the distinction between carbon and osmosis matters.

Faucet holes, space, and installation

The practical question that always arises after the technical one: can it fit in my kitchen? Three things determine that.

The countertop. Drilling a second hole is a routine job in stainless steel, plastic, and wood. It can also be done in granite, composite, and ceramic, but requires the right drill bit and more caution; sometimes a 3-way tap in the existing hole is simply the wiser choice. Many sinks already have a second pre-drilled hole covered with a cap, originally intended for a soap dispenser.

The space under the sink. An undersink system requires space next to the siphon. This is usually not a problem, unless there is already a waste bin drawer or a water softener. If you want to know what an osmosis system requires from your base cabinet and what trade-offs are involved, you can read about it in the overview of the downsides of osmosis.

The connection itself. The system connects to the cold water pipe with a branch, a shut-off valve, and a drain connection for the rinse water. PureAqua standardly has this done by a specialist; those who are handy can use the 49-euro DIY installation kit. That is more than just convenience: as shown above, the modification must comply with the principles of NEN 1006 and the requirements regarding backflow prevention, which is exactly what an installer is for.

What does a separate tap for filtered water cost?

The water itself costs almost nothing. According to Vewin, you pay an average of 2.71 euros per cubic meter of drinking water in 2026, including taxes, which is approximately 0.003 euros per liter. The costs of a separate tap therefore lie entirely in the tap, the system, and the filters.

At PureAqua, a 1-way tap starts at 149 euros for The Wave, with most priced between 465 euros and 495 euros; 3-way taps range from 590 euros to 840 euros. An important detail in the sales model: the undersink system The Source cannot be purchased separately, but is included as standard with a pure water tap. Therefore, you do not pay twice. The 495-euro Countertop RO is separate and does not require a tap.

For maintenance, you pay for a filter set. A set of two filters costs 75 euros, a set of three 149 euros. Those who prefer not to keep track of anything can choose the "Zorgeloos Zuiver Water" (Carefree Pure Water) subscription: 29 euros per month with a 299-euro start-up fee, including a tap of your choice, the filter system, filters for twelve months, and installation by a specialist.

Compare that to bottled water and the calculation quickly shifts: one bottle per day means hauling, paying for, and discarding over 350 bottles per year. Milieu Centraal calls tap water the most sustainable beverage choice you can make, and a separate tap is exactly the way to make that tap water delicious and scale-free.

Which setup fits your kitchen?

Your kitchen is brand new and the tap looks great

Then you don't want to replace that tap. Choose a 1-way pure water tap in the same finish, so that the two taps side-by-side form a cohesive unit. PureAqua offers stainless steel, chrome, black, gunmetal, and gold, so matching is almost always possible.

You are going to renovate or update your kitchen anyway

Then a 3-way tap is the logical choice: one hole, one tap, three flows. Include the filtered water in the design right away, as drilling an extra hole in a newly installed composite countertop is much less pleasant than having it done beforehand.

You have a Quooker or want boiling water

Boiling water and osmosis water come from the same design or from two separate tap points at PureAqua, never from a converted Quooker. The 4-in-1 tap replaces the boiling water tap and additionally provides filtered, filtered boiling, and filtered chilled water. If you really want to keep your Quooker, a separate 1-way tap next to it is the clean solution.

You are renting, or you are not allowed to drill

Then every tap option is ruled out, and the Countertop RO remains. No hole, no modifications to the plumbing, and when you move, you simply take it with you.

Your concern is limescale throughout the house

Then a separate drinking water tap only solves half your problem. A tap point treats one location; limescale on your glassware, in your dishwasher, and in your central heating system requires a central water softener. According to Vitens, the average hardness in the Netherlands is around 8 dH, which is soft to moderately hard; water companies only refer to it as hard water above 12 dH. Many households therefore primarily have a drinking water need and not a softener problem.

Frequently Asked Questions

Conclusion

A separate tap for filtered water is not a design choice but a technical necessity. Mixing undoes the purification, hot water damages the membrane, the pressure behind the membrane does not match a standard mixer tap, and the Dutch installation rules regarding backflow prevention and NEN 1006 are much easier to meet with a separate circuit. Everything that comes after that is just about form.

That form depends on two things: how many tap holes you have or want to create, and whether your existing tap can stay. If it stays, a 1-way tap point is the neat solution. If you are going to renovate, a 3-way tap is the sleekest. If you also want boiling water, the 4-in-1 tap does everything from a single design. And if you are not allowed to change anything in your kitchen, the Countertop RO provides the same water without turning a single screw. PureAqua is happy to help you see which of the four fits your kitchen. Drink different.