There is actually a specific solution for this: https://www.homedepot.com/p/Chronom...Amp-120-Volt-1800-Watt-SR-15L-120-I/307248643After 40 plus years, I just realized that my wife turns the faucet knobs to full HOT every time she rinses her hands... for a few seconds. The HOT water runs about 20' in the plumbing and stops there to cool down to room temperature. I'm not concerned about the habit... just that it took me 40 years to notice the energy waste.