You can stop most of the hot water waste in that situation with one of these [1]. It's a valve that you put ahead of the shower head. When it senses that the wa

You can stop most of the hot water waste in that situation with one of these [1]. It's a valve that you put ahead of the shower head. When it senses that the water has warmed up to 95℉ it reduces the flow to a trickle until you turn a lever to restore full flow. [1] https://www.showerstart.com/products/showerstart-tsv3 https://www.showerstart.com/products/showerstart-tsv3