can I use a 120 volt water heater on a 240 volt circuit

There's a good chance the internal insulation of the element will thermally isolate it well enough from the cooling water to burn out the element.

Blowing the breaker is another possibility depending on the wattage of the heater.

No, it's not going to work. I would use the step down transformer if you must or just get one over there.

yeh, get one there cause of the different socket configurations.

For a given resistance R, and a given voltage V, the current (I) in amperes is given by I=V/R. Also, the heat produced in Watts in given by the the square of the current times the resistance. Thus if you double the voltage, you double the current, and the heat produced is 4 times greater than normal. The heater will burn out.

I understand the risk of additional heat, but I'm still wondering if the use of a 120 volt device (assuming the water can dissipate the heat fast enough so it doesn't burn out) will result in any significant additional current which may blow a fuse or trip a circuit breaker. If the answer is already embedded within the I=V/R equation, I'm sorry, but I'm not sure how to solve it. The heater is 1200 watts so (I think) that means, on a 120 volt circuit, it's drawing 10 amps? If I double the voltage, does that mean it'll then be drawing 20 amps?

You will draw twice the current, This does more than just generate heat in the coil. It also generates heat in all the wiring, the enclosure and all the switches that control the device. THIS IS A BAD IDEA.

If you are trying to understand this fundamentally, I have one more thought for you. Heat transfer is proportional to the temperature difference between the water and the coil. Since you are trying to move four times the power the temperature differential will be four times higher. That means if the water is 100° C and the coil was 200 degrees C the coil will now be 500 degrees C.

More technical details that probably don't matter:

If the heat flux between heater and water is too high, which is no doubt going to happen as the water heats up, the element will experience 'film boiling' which isolates the heater from the water and the temperature of the element will skyrocket.

These things are not designed any more robustly than they need to be, to sell at a market price. The heater element will be designed and sized to suit the electric supply. Say it has a 500 Watt element that draws around 4 amps at 120 volts if you double the supply voltage you now have a inadequately built (and insulated) 2,000 Watt element, which will draw 8 amps at 240 volts. If this does not trip the breaker supplying the circuit, the element will get much too hot, much too fast, and may self destruct. It may have a thermal cutout, such as a fusible link (a part of the element made of low melting point metal) or if not, expect noise, steam and possibly flying bits of coffee pot.

Thanks for all the input. Message received. Now, anybody have a 240 volt coffee pot they can loan me?