With this is in mind, we decide to make the controls to the game very minimal. We chose to try out left and right movement as the core mechanic at first. This would require the user to wash their hands while slightly move their hands from left and right within the sink to play the game.

Left and right controls are simple and allow the user to wash their hands at any speed they want.
...but we ended up changing the controls for the installation to be the speed at which the person washes their hands. In other words, the Leap Motion will pick up how fast your hands are moving and based on that, it will affect the mechanics of the game.