Been to an air plane loo recently? I bet you have. Thought about the flush button in there? Unfortunately, you might have. That's due to it's poor interaction design.
Using the same volume of water for all flushes is wasteful. Perhaps using water at all is too wasteful for the planet. But using a toilet where there is a choice of a small or a big flush is, I imagine, a small step forward. 6 examples of flush buttons.
Over the last 100 years, bathroom and kitchen faucets have become very common. Have you thought about how much they have changed over time?
I had the pleasure of staying in the UFO at the Thee Hotel over midsummer. Since the room is suspended between three pines there is no running water. Instead, there are shared showers in a separate building. And an incineration toilet in the UFO.
Some shower faucets have more then one outlet – one for a shower head and one for filling the bath tub, for example. In these, the water temperature and water flow is set once and a lever is used to switch between the outlets. The design of that switching mechanism can be quite horrid.
Use the human ability to see connections between separate parts of a system. Build products that help us improve the world a bit. Build accessible artefacts. Make the important system states obvious. If your interface needs instructions, you have failed.
Some companies try to understand how satisfied I am with their public toilet. I don't think their method works. A new button can help.