This is a first-draft prototype of a slider control for a shower. The control is intended to move easily between warm and cool, with a double-reversal of direction required to select very hot or very cold water. The control utilizes some fundamental interactive properties. Water temperature is mapped to up and down, and constrained from accidentally entering unintended extreme regions. However it does break the cultural convention of having hot water on the left. For a revised version, I would follow the convention, and also add icons with conventional red and blue coloring. It would be interesting to test whether the knob could successfully act as a multi-function control to regulate water volume. My hunch is that it would be superior to have a second control instead, perhaps a lever that moved up and down. The prototype was fashioned with wood using a scroll saw and with a stereo knob on a screw using washers to help it slide.