For example, too much voltage will burn out an LED, so how does that relate to the water metaphor?

The pressure from the water hose would do a number on you, just as voltage does bad things to the LED; but it's actually the overcurrent that follows from the overvoltage that does the job, same as the pressure in a fire hose feeding through a pinhole won't harm you, but a 2" firehose fully open will knock you over... With high enough pressure/voltage, even small flows/currents will be dangerous though - think waterjet cutting machine...

But LEDs are a bit odd - they're better controlled by controlling the current run through them than by controlling the voltage fed to them. This is because small differences in voltage lead to large differences in current...

But take a normal lightbulb; it can handle a given voltage - like a hose that can handle a given pressure. It will pass a given current at the rated voltage, as the hose will allow a certain water flow at the given pressure.

/Michael