Shower time limit
There exist technology and hardware that facilitates for a put shower time automatically. It can easily be installed to your current system, where you decide how many minutes each shower is going to last. Lets say you put it at 5 minutes, during the shower it will signal to the guest how much time is left. After the 5 minutes it will stop automatically and not start again for another 5 minutes, motivating guests to finish up before the first 5 minutes are over.
Maresias Hostel in São Sebastião installed this system at one of their showers and tested it out for 6 months. The vast majority of the feedback from guests were positive and they are in the process of converting more of their showers to this system. They say they will save a lot of money on their water and energy bill in the long run, as well ass contributing to the responsible and sustainable water handling the world needs.