[fjcaetano]

There's no need for electric showers. The heat regulator could be attached to the "cold" and "hot" handles and a thermometer at the output of the shower.

When the temperature differs from the setup it automatically adjust the "hot" or "cold" temperature to regulate it.

The problem with this is that the whole system would be "reactionary", meaning that temperature regulations would only happen AFTER temperature alterations.

[sokoloff]

That's true of HVAC thermostats as well, and works OK in that application.

[njharman]

Yes but hvacs aren't spraying scalding or (worse) cold water on your half-awake self.