Showers

It's days like this that remind me that the the ground pipes holding the water aren't that well insulated and that my shower just turns a heater on and pumps water through it rather than measure the inflow or outflow temperature - brrrh!

But the heat exchange coefficient of water is known, the flow of water is controlled, the temperature of the inflowing water can be measured, and the temperature of the heater can be set. So there's no reason why the temperature of the outflowing water can't be maintained at a constant without recourse to twiddling dials.

I suppose it's expense, but it's the 21st century and this is still the most common control method - yeesh!