Sometimes, the environment encourages you to ask questions:

Three taps are generally uncommon, I've actually rarely ran across such an installation; that one has been spotted in Geneva, in a restaurant close to me block. So, three handles: one for the hot water, one of the cold water and the third one without any feedback when employed. Still, it's there, part of the design and definitely connected to the cold water valve. Besides, there's also a second hole.

Was it meant to be a strategy or a shortcut to get cold water more rapidly? Some complex feature to control the mixing of hot and cold water? Or was it just because the owner broke something and only had this to fill the gap between different parts.

Then, how this relates to design or ubiquitous computing? IMO, what is intriguing here is the relationship people have with technologies. What happened when people looks at this object? well, in the context of this interaction, I washed my hand and - of course - tried to open that handle to see what happened. The presence of this third handle (that I would qualify as an intru) definitely raises curiosity. Such an interface may interfere with the task at hands, not in this case because the interaction is very simple. Moreover, in such standardized setting, it clearly stands out as a focus of attention, there is a clear affordance to use it. But then nothing happens, how mysterious.