The Water Treatment Tap: Single-Flow or Three-Way?

Hours are spent comparing membranes, stages and capacities when choosing a unit. Against that, the smallest part in the box is often never discussed — yet it is the only component touched by hand dozens of times a day. A few months later the lever starts to move, drips come from the spout and a permanent mark forms on the worktop. So a water treatment tapis not an accessory to the unit but the part at the centre of the experience of using it.

In this guide we take up the tap side: the difference between single-flow and three-way, the worktop hole and layout conditions, the effect of body material on durability, connection compatibility, the reasons for dripping and when to replace it. We do not go into the installation steps; the focus is on the tap itself.

Why Is a Water Treatment Tap Fitted Separately?

Treated water comes through an independent line leaving the unit. That line does not mix with the mains connection of the kitchen mixer; so a separate tap is fitted to the worktop. That tap gives only treated water and is connected directly to the outlet line of the unit.

The technical reason for the separation is simple. A kitchen mixer works by mixing the hot and cold mains lines; treated water, on the other hand, is delivered through a separate line after passing through the stages. The two flows mixing in the same body would remove the definition of treated water.

On systems with storage that line is fed from the tank. When the tap is opened, the air pressure in the tank pushes the water and the flow starts; so the flow character of the tap is related to the tank structure of the unit too. The storage tanks widely used on domestic installations are the component feeding that line.

For the general framework of point-of-use treatment units, the US Environmental Protection Agency point-of-use and point-of-entry treatment units resource can be consulted; it defines systems where the treatment is done at the point where the water is used.

Which type of unit to choose is a separate subject; we took up the criteria in our unit selection guide . The scope of this article is the last link after the unit: water treatment tap and the connection side.

The Difference Between Single-Flow and Three-Way Taps

Single-flow models give only treated water and are fitted to the worktop through a separate hole. Three-way models bring hot, cold and treated water together in one body; that way an extra hole in the worktop may not be needed. The choice is made according to the state of the worktop and the kitchen layout.

The two types do the same job with a different logic of layout. The distinction runs like this:

The deciding point is usually the worktop. If there is a suitable empty hole in the worktop, or if a new worktop is being made, a single-flow model is used easily. If you do not want an extra hole made in an existing granite or composite worktop, a three-way model can remove that need.

There is one detail to watch on three-way models: the treated water line runs through a separate channel inside the body and does not mix with the mains water. The three-way tap models offering that structure are preferred by those who want to work with a single fitting in the kitchen.

The comparison of the two types can be summed up like this:

The last row of that table matters over the long run. When a single-flow water treatment tap fails, only that part is renewed; on a three-way model the whole kitchen mixer is involved.

Figure 1: Single-flow and three-way taps compared

The Worktop Hole and the Layout

Before installation it is checked whether there is a suitable hole in the worktop. Some worktops have an unused blanking hole ready. Where a new hole is needed, the operation carries a risk depending on the worktop material and must always be done by a specialist.

That is the most critical heading in the installation process and the one where most mistakes are made. The worktop material is decisive here.

The position by material can be summed up roughly like this:

On the layout side two points are assessed: the position of the tap relative to the sink and the cabinet space beneath it. The tap should be in a position where the flow falls into the sink; and there should be enough room inside the cabinet for the connection at the underside of the body.

There is a practical suggestion for those having a new worktop made: the hole for a water treatment tap should be planned while the worktop is being manufactured. That both removes the risk and creates no extra cost.

The Tap Body and Material Quality

The body material and the durability of the finish directly settle the working life of a tap. The quality of the cartridge and the gaskets in the internal parts affects how it behaves for dripping. On low-quality products, the finish coming away and early dripping are problems met with often.

This part is opened and closed dozens of times a day. A moving mechanism, constant contact with water and constant contact with hands come together; those three conditions make material quality decisive.

The headings to assess are these:

• The body material: The structural strength of the body, which works under pressure, is what decides.
• The finish: The durability of the surface finish affects the staining and flaking that occur over time.
• The cartridge / mechanism: The quality of the opening and closing mechanism settles how it behaves for dripping.
• The gaskets: The sealing parts come first in preventing leaks.
• The internal channel: The inner surfaces the water touches are expected to be made of suitable material.
• Spare parts: Being able to obtain the gasket and cartridge separately makes the product repairable.

The last item is often overlooked. On a product whose spare parts can be found, when dripping starts only the gasket or the cartridge is renewed; on a product whose parts cannot be found, the whole tap is changed.

When choosing among the treatment tap models offering different bodies and finishes, those technical headings should be assessed as well as the appearance.

We took up what component quality means across the unit as a whole in our component guide ; here we focus on the tap side alone.

Looks and Fitting In With the Kitchen

A tap is a part constantly on show in the kitchen, so how it goes with the existing mixer matters. Chrome, matt black and stainless-look options are common. The height of the body and the direction of the flow should suit the depth of the sink.

Assessing looks is personal; but it can be done through a few concrete headings.

The first heading is matching the finish. If the kitchen mixer is chrome and a matt black fitting is added beside it, a visual mismatch appears. Preferring finishes from the same family gives the worktop a coherent look.

The second heading is the height of the body. A tall body makes filling jugs and large vessels easier; against that, it can create splashing in a shallow sink. A low body reduces splashing but can make filling large vessels harder.

The third heading is the direction of the flow and the ability to swivel. On some models the body turns horizontally; that gives access to different points in the sink. That feature is a practical convenience in wide and double-bowl sinks in particular.

And finally the position: placing the tap too close to the mixer can lead to your hand catching it in use. When planning the layout, a comfortable working distance should be left between the two fittings.

Figure 2: The tap connection under the worktop and the sealing parts

Fittings and Hose Compatibility

The tap hose has to be compatible with the outlet of the unit; the connector size and the connection type have to match. A significant share of leaks comes from connections that are not fully seated and from tired gaskets. So the connection points call for as much care as the tap itself.

Because that heading stays inside the cabinet it is the least noticed area but the one that causes the most trouble. However good the tap body is, a leak forms where the connection is not made correctly.

What should be checked for compatibility is this:

The last row of that table is a common mistake. A hose trapped inside a cabinet or making a sharp turn both restricts the flow and creates structural weakness over time.

We took up the steps of the installation process and the mistakes made most often in our installation guide ; we do not repeat the steps here.

The practical rule on compatibility is this: when buying a new water treatment tap , the model of the unit and its outlet connection type should be stated. Once that information is shared, the risk of an incompatible part largely disappears.

What Should Be Done if the Tap Drips?

Dripping generally comes from four causes: the gaskets tiring, the opening and closing cartridge wearing, the connection points loosening, and the line pressure being high. To tell the source apart, where the drip is coming from should be observed; where you cannot be sure, a technical service should be called.

Where the drip comes from largely explains the cause. The table below matches the sign with a likely cause:

The last row is a heading of its own. If the line pressure is above what is expected, the connection points are strained and the risk of a leak rises. We took up the diagnosis of pressure and how it is assessed in our pressure article .

The check a user can make is at the level of looking: where the drip is coming from, whether there is damp under the cabinet and whether there is movement in the body. Taking things apart beyond that falls within the scope of technical service.

When Does a Tap Need Replacing?

Replacement comes onto the agenda when signs such as constant dripping, the finish flaking, permanent movement in the lever and a marked drop in flow appear together. If the unit is sound, only the tap can be renewed; there is no need to change the whole system for that.

The most important thing in this section is this: the tap is an independent part. If the unit is working without trouble and the tap has worn, only that part is changed.

The signs that bring replacement onto the agenda are these:

The fifth card is the result of the decision made at the buying stage. On a product whose spare parts can be found, dripping is solved with a small piece of maintenance, while on a product whose parts cannot be found the only option is replacing the whole thing.

We took up how the components of a unit age at different rates and how the repair-or-replace decision is made in our unit lifespan article . The tap is one of the parts in that picture that can be renewed on its own.

The point to watch during a replacement is compatibility: the new water treatment taphas to be compatible with the outlet connection of the unit and with the existing hole in the worktop. Once those two are clear, the change goes ahead without trouble.

Its Relationship With the Final-Stage Filter

The final-stage filter sits between the unit and the tap; the water passes through that stage before reaching the tap. So the choice of tap does not affect the filter build, and the choice of filter does not settle the type of tap. The two are independent decisions.

That distinction is a point users often confuse. The answer to “if I am going to use a mineral filter, do I need a special tap?” is no.

The order of the line is this: the stages, the tank if there is one, then the final-stage filter and the tap last. The tap is only the outlet point of the line; it does not change the character of the water passing through it.

Whether a cartridge containing minerals is used at the final stage is a separate preference. We took up what that stage does and what it does not in a balanced way in our mineral filter article article.

The practical conclusion: there is no need to think about the filter build when choosing a tap. What is decisive is compatibility with the unit outlet, the state of the worktop and the quality of the material.

How Is the Right Water Treatment Tap Chosen?

Five headings are assessed in the choice: compatibility with the unit outlet, the state of the hole in the worktop, fitting in with the kitchen, the quality of the body and internal parts, and the availability of spare parts. Once those five are clear, the right model is easily established.

The checklist below covers the items to complete before deciding:

If you can answer those nine items, the choice is largely settled. The only thing left is a preference about appearance, and that is entirely a personal decision.

Water Point Su Arıtma Teknolojileri operates from Esenyurt, İstanbul under its founder Ali Genç, with more than 20 years of experience in the sector.

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