I am currently trying to come up with an intuitive design for a touch free sink faucet that allows for both hot and cold temperature settings. Most touch free sinks involve one sensor to start the water flowing and you're stuck with whatever temperature comes out, which is usually just a mix of the two. After some research I found some designs incorporated a knob on the side to allow temperature settings, however in public restrooms a truly hands free design is strongly desired even if youre about to wash them, hence the invention of hands free soap dispensers even though it is putting sanitizing soap on your hands after touching it.

The initial design I thought of was something like this: enter image description here

The user puts their hand over red sensor to start hot water, blue to start cold, both to start medium.

However, there are some obvious oversights:

  1. The sensors aren't in front of the faucet, so they will keep stopping forcing you to wave over them again.
  2. The "medium" setting is not very intuitive

To fix number one I added the middle black sensor, that way you activate the temperature states first by waving over the colored sensors, and then the water starts when you wave in front of the black one like typical hands-free faucets.

However, I believe this to be even less intuitive and too many steps to simply wash your hands.

So, are either of these designs intuitive or is there a more streamlined and easily understandable way to incorporate hot and cold functionality into a truly hands free faucet?

  • 2
    As a frequent faucet user, I want the temperature to be immediately ideal for washing my hands, not have to adjust it by turning a knob or flailing my hands. For optimum user experience, just pump out water at the correct temperature rather than forcing me and every other user to keep selecting it.
    – Paul S
    Mar 23, 2016 at 22:41
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    @PaulS while that would be ideal, if I learned anything from my girlfriends boiling hot showers is that "correct temperature" varies from person to person. Now sure there is probably a tolerable range of temperatures that would suffice, but in UX when do we settle for tolerable!
    – DasBeasto
    Mar 23, 2016 at 22:49
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    Just curious, why is non-touch preferred even prior to washing? Psychological thing? People perceive it as unpleasant to touch something, even if they're about to wash their hands?
    – Fiksdal
    Jul 20, 2016 at 7:15
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    @Fiksdal People just perceive it as a "gross" thing, everything in a bathroom is "tainted". Its similar (hyperbolically) to asking someone if they'd stick their hand in the toilet right before washing their hands, even though they'd wash off whatever filth they got on them you'll find no one would volunteer.
    – DasBeasto
    Jul 20, 2016 at 12:27
  • @DasBeasto Yes, good analogy.
    – Fiksdal
    Jul 20, 2016 at 15:47

5 Answers 5


Just so you know, here's how your color coding looks to those with protanopia, the most common form of red/green colorblindness.

enter image description here

  • Isn't this a problem with every single faucet/tap ever designed?
    – Midas
    Mar 23, 2016 at 17:56
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    Not if you add a third black option which will look identical to the red option to some people. Mar 23, 2016 at 18:39
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    @EricStoltz that middle black option is intended to just be an inlaid small sensor like you see on faucets now, it just looks like the others due to my limited MS Paint skills. I do see your point though I'd likely have an H and C on the red and blue to differentiate, and maybe use an orange-ish instead to help further.
    – DasBeasto
    Mar 24, 2016 at 11:58
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    Blue snowflake and red flame. Color-blind people also aren’t stupid: they’ve learned early on that when blue opposes something in a water context, it means cold and the other side means warm or hot (and looks red to other people). Also, the sides are standardized in many cultures, e.g. cold is on the right-hand side in most of Europe.
    – Crissov
    Apr 4, 2016 at 7:33

When I am washing my hands at work I get a choice of pushing the Hot or pushing the Cold, there is no Medium. I wish I had that choice.

I would like Medium to be the default - when I place my hands under the faucet, give me Medium while my hands are there.

If I wave on the left side of the faucet I would like it to get warmer. If I wave on the right side, I'd like it to get colder.


Interesting idea DasBeasto, have you considered leaving the center sensor and having a user wave their hands as normal under the faucet and having the usual/expected result of water coming out.

But you then have a separate temperature sensor on the side of the faucet that allows you to select cold, medium or hot temperatures.

Almost exactly like this variable temperature, sensor faucet - but using a sensor rather than a dial: variable temperature motion sensor faucet

As for the color indicators, I would like to see a blue or red light shine from behind a 'C' or 'H' cutout - that way you have color and letter indicators (maybe use amber and 'M' for medium temps).


A very interesting question, and I like thinking about these things because the two-dimension-ness of most UI design questions don't trigger enough areas of the brain for creative thinking!

I know this is probably the more 'expensive' of the solutions, but I think what you should be doing is separating the controls from the indicators, which is a common problem with user interface design.

I would think of having an area in the middle that acts as an indicator for the temperature of the water, and use H/C combined with the colours to avoid confusion. This would be in the form of a gauge like:

H --|-- C

with the marker '|' to indicate the current temperature setting.

Then you would have a sensor on either side of the faucet marked 'H' and 'C', and when you put your hand over either one of the sensors, it moves the marker towards that side of the gauge. That way when you put your hand under the tap it would still just trigger the water to flow.


You’re looking for a solution without a proper description of the problem. Apparently the default water temperature pouring from the faucet is too hot or too cold for some people in some situations.

  • Can it be either or is the temperature off in just one direction?
  • Does the default temperature vary throughout the day or year or some other factors?
  • Which precision and consistency can the plumbing and heating system guarantee?
  • Is there a tolerable temperature range for everyone?
  • Are you designing for a specific use case and user group or is it a general design that shall be selectable at the architect’s or plumber’s discretion?
    • Do you have mostly regular, returning or random users?
    • Is the sink only used to wash their hands after using the toilet?
    • Is a certain gender, height, age or other group over-represented?
      (Public restrooms are often separated for male, female and handicapped. The optimal design choices may very well differ for them. Small people, predominantly children, often cannot access standard faucet controls easily by themselves.)
  • Could alternate controls offer a better discoverability, accessibility, usability, efficiency and hygiene, e.g. foot-operated pedals?
  • Are you designing just the controls or the outlet and sink, too?
    Does the faucet have to be pipe-like or could it be broader, waterfall-like?
    The latter would allow a sensor array (maybe with color LED feedback) integraded into the faucet instead of the sink surface.
  • If the water stops, e.g. while applying soap, will it continue afterwards with the previous or the default temperature?

That being said, and assuming invisible controls are acceptable in the intended scenario, e.g. because they already have been learned by the populace, it’s certainly a good idea to start off with the common design, i.e. support the default temperature in the middle. I strongly suggest to first optimize the default before introducing user adjustments.

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