Hot Water heater wall switch

I would like to install a wall switch that will turn my electric hot water heater on and off.  I can't seem to find instructions online. Any ideas?

Many thanks.

The National Electrical Code requires that an electric water heater have a disconnecting means within sight of the heater with one exception. 

So, generally, there should be a way to shut off the water heater already present.

Electric water heaters generally draw a large current which requires any disconnect switch to be stronger and larger than the average "wall switch" (the average wall switch is rated for a maximum of 15 Amps at 120 Volts).  A switch for a common electric water heater, by comparison, might be rated at 30 Amps at 240 Volts.  That's an increase of four fold.

To try to answer your question, it would help to know the kiloWatt rating and the location of your water heater, as well as where your electrical service is, and the Amperage and Voltage of the water heater's circuit.