I had stayed in many hotels around the world. Most of them have hot and cold water system in the bathroom that are not easy to use. They forget that the hotel guests are usually visiting their hotel for the first time.
One frequent problem is that, if you have just used the soap, you are not able to turn the knob of the taps.
Recently, I visited the Conrad Hotel in Brussels. It has a user-friendly system for hot and cold water. You use one control to decide on the temperature of the water and a separate control for the volume of the water, i.e. to turn on and off.