I disabled our shower by forcing the taps shut with spanner, the tap washers I prefer are ok for this.
Attached a shower head hose to the bath tap, so now all we have is a shower head you have to hold and mostly sit or squat to use it.
This has eliminated certain individuals from emptying the hot water system while washing their hair, and my own tendency to use a fair bit of hot water while standing in the shower.
Bit of a hack, YMMV.