Why are double-handle taps still installed in households and public washrooms?

Question

I'm wondering why double-handle faucets are still installed in sinks, bathtubs, etc in newer places of dwelling as well as public washrooms. From reading, they appear to be easier to install, but surely this can't be the only reason.

I can understand the uses of double-handle faucets in commercial environments (e.g. restaurants), but at home they are really inconvenient:

• They require either two hands to operate or twice the amount of time when operating them sequentially with one hand.
• They waste a lot of water when you are trying to get a precise temperature (there goes 200 L of water and I still haven't gotten into the shower)
• They provide two points of failure in the case of a leak
• Where labelling is required (e.g. hotels), the labels "H" and "C" aren't easily internationalized, though you could use blue and red
• Teaching children how to use a tap seems generally more difficult with double-handle faucets

In public washrooms, patrons generally just want to wash their hands. In some areas, laws require the water to be a certain temperature, but again, compliance can be achieved by setting the temperature of the water for a mixer tap.

I've seen two designs of mixer taps, where they either go from cold to hot, or there is a default position in the middle and left is hot, right is cold.

Has there been a study on this or are there points that I'm missing from a UX perspective?

---

For reference purposes:

Double-handle faucet - Two knobs that allow you to control the volume of hot and cold water independently

Mixer tap (single-handle faucet) - One knob that allows you to control the volume of water.

Answer 1

Going from a two-tap system to a mixer system often means replacing the porcelain sink itself. This is a much more costly proposition than simply updating the hardware; the new sink is expensive, you need to cart away the old one, and you may need to open up the wall to install the new one.

Style is also a primary reason. For some people, the look of the two-faucet style indicates quality, or heritage, or simple familiarity.

Finally, it is easier for some users (e.g., kids) to use the cold-water tap with no chance of scalding.

Answer 2

There are actually three varieties:

1. Mixer tap, with one handle
2. Mixer tap, with separate hot and cold handles
3. Two completely separate taps, such that the hot and cold water only mix in the sink

Obviously, Type 1 is most convenient.

Type 2 does have an advantage in energy savings. Often, with a single handle, a user will leave the handle somewhere in the middle, such that it draws water from both the hot and cold pipes. However, the hot-water draw is often unintentional. The user will just wash his/her hands for a few seconds, not long enough for the water to get warm, and not really caring that the water is cold. Nevertheless, drawing cooled water from the hot side does have a consequence, since the hot water tank will need refilling. Therefore, users of single-handle mixer taps will often unknowingly waste energy heating water for absolutely no benefit. (The Swiss government, for example, runs a campaign to remind people to keep the lever turned all the way to the right, which would not be necessary with a two-handle system.)

The British, though, seem to be stuck on Type 3. Part of the reason is a fear that a dirty heater tank could contaminate the cold water supply if mixing were allowed. Mostly, it seems to be a case of stubborn conservatism.

Answer 3

Single handle faucets are very handy indeed because they give independent control of (i) the flow and (ii) the temperature.

Among the relative advantages of two-handle faucets, one can mention :

• style : although subjective, some are sensitive to their style and prefer them over single-handle faucets when they favour an old-looking style
• ease of use to tap either cold or hot water : being able to easily tap either as-cold- or as-hot-as-possible water is a frequent need in some places, e.g. kitchens. This assumes that handles are efficiently characterized, namely with widely agreed conventions like red and blue markings.

Answer 4

Double handle faucets are much easier for people with reduced motor capabitlies to operate. I've seen them accompany the handicapped stall in restrooms.

Answer 5

"Type 2 does have an advantage in energy savings. Often, with a single handle, a user will leave the handle somewhere in the middle, such that it draws water from both the hot and cold pipes. However, the hot-water draw is often unintentional. The user will just wash his/her hands for a few seconds, not long enough for the water to get warm, and not really caring that the water is cold. Nevertheless, drawing cooled water from the hot side does have a consequence, since the hot water tank will need refilling. Therefore, users of single-handle mixer taps will often unknowingly waste energy heating water for absolutely no benefit. (The Swiss government, for example, runs a campaign to remind people to keep the lever turned all the way to the right, which would not be necessary with a two-handle system.)"

In 3rd-World countries, this is a big deal because the cold water tap is completely adequate in the vast majority of usage (these countries are usually tropical and have warm "cold" water), but because people leave the lever in the center for aesthetic symmetry, a huge amount of heat is wasted for no benefit.