The scientific paper "show-me": Water Consumption at a Glance to Promote Water Conservation in the Shower [acm.org, ACM members only] aims to encourage sustainable behavior by visualizing the actual water consumption when and where it matters: during and immediately in the vicinity of the showering itself.
The researchers built a prototype to study the potential of such a feedback device in the form of "LEDs assembled on a stick". In the study, ecologically conscious participants showed positive behavioral changes (i.e. mean water consumption decreased by approximately 10 liters), although this was not maintained after the removal of the display.
The paper is based on the assertion that ambient displays are suitable for a constant and subtle persuasion by providing continuous and unobtrusive feedback. show-me gives the user feedback and an impression of the amount of water going down the drain. This impression is achieved by exploiting the metaphor of the drain being closed, and the water level increasing within the closed shower. The imaginary water level is visualized in the form of LEDs that are vertically assembled on a stick. During operation, one (additional) LED is lightened up for every five liters of water consumed. In multiple different trials it was discovered out that an amount of 5 liters per LED was ideal: a high water consumption would stay within the 16 LEDs limit, while a lower water consumption is still sensibly shown within 4 to 6 LEDs.
"The prototype also triggered some interesting side effects. A couple used to argue that one of them always took longer in the shower and consequently used more water. After they installed the display, they learned that the woman used only half as much water, even though she spent more time in the shower. This discovery stimulated the man to further reduce his own water consumption."