Dual flush: interface design gone down the drain

For some time now, I have been thinking about dual flush toilets. I find them annoying, or rather: I find their interface annoying.

Their intended purpose is good: not all visits to the toilet require the same amount of water to flush, so why empty a whole cistern every time? Dual flush allows us to save water, which is good for both the environment and our pockets.

However, every time I see one, I am at a loss as to how to correctly operate it. Is is the large portion of the button that I have to press or is it the small one?

Regional disclaimer: In Europe, every dual-flush I have seen has a button-based interface. I hear there are lever-based ones in other parts of the world, but I cannot comment on those.

Initially, it would seem reasonable that the large portion is intended to release more water. That sounds simple enough, right? Well, no, because the small portion is often so small or narrow that it is difficult to press it without accidentally pressing the other one in the process.

Therefore, thinking that the opposite is true would also make sense. After all, if you are going to press one of the buttons accidentally, it better be the one that uses less water. You’d then make this be the larger button. Then the smaller button would be pressed by users who are certain they require to spend the whole cistern.

I have been so bothered with this lately that I have started to study them. Unfortunately, this forces me to spend more time in the toilet when I am in a new place, but it’s all for science! :-)

Whenever I see a dual flush, I bring out the chronometer on my mobile phone. I press one of the flush buttons, time how long it takes to operate, wait for the cistern to fill back up, and try again with the other button. Normally several times, just to make sure.

Funny thing is: I have barely done any progress because most of the time both options seem to take as long to operate! So not only the buttons are badly designed, but also the feedback (the appearance of the resulting stream of water) is all wrong and hardly gives any information as to what actually is going on.

Not all designs I have seen are as bad, but in general the landscape in this field is pretty depressing. The best designs I have seen are not really good, but just less bad. For example, recently I saw this one at a restaurant:

In this instance, pressing the lower portion resulted in a short flush, whereas pressing the upper portion resulted in a long flush.

I am not sure if you can appreciate it well in the picture, but the lower portion is bulging out, whereas the top one has a hollow shape, as if sinking away from the user. This makes the lower portion easier to press. Additionally, there is one clear mark on the lower one and two on the upper one, but easy to see and touch evident. Also, the upper portion is slightly larger, as the lower portion has the typical crescent shape, but less pronounced than in other examples. This should follow the idea that the larger surface creates a longer flush.

However I think this is not good enough. The size of each portion is still small, making it accident-prone. Less so that other common designs though, but when you press a button and it sinks in, it’s not trivial to avoid pressing the other one.

Also, I wonder how evident the meaning of the markings is. In my mind it makes sense that two markings mean “more” than one, and therefore should release more water, but what do other people think? After seeing how bad these interfaces normally are, I wonder if their creators ever bothered doing any user testing at all.

But anyway, I’ll continue doing my research. To some it may seem silly toilet humour but, for something that plays such an important role in our lives, I think it’s important to get it right.