hi there
I am sharing with you this device we have installed in our apartment to control our guest's showers: Acqua Tempus
it is simple to install and program and restricts the maximum shower time, after which, it shuts the shower off and leaves it off for a pre set waiting time, so the tennant must leave
once this waiting time has passed, a new shower is available
we are in Spain, a dry country, we don't have much rain in here so any thing we can do to reduce water consumption is always welcome
you can check this shower timer here: https://www.youtube.com/watch?v=z7FrueY_kcw&t=16s
It is now two months since we installed it and the water and electricity bill have dropped , and we don't have guests complaining for running out of hot water.
100% recommendable
I hope this thread helps
Regards